Spinal Cord and Spinal Nerves

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Spinal Cord and Spinal Nerves

• Chapter 12

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Spinal Meninges

• Connective tissue membranes surrounding spinal
  cord and brain
• Dura mater continuous with epineurium of the
  spinal nerves----thick
• Arachnoid mater thin and wispy
• Pia mater bound tightly to surface of brain and
  spinal cord.

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Cross Section of Spinal Cord

• Roots spinal nerves arise as rootlets then
  combine to form roots
• Dorsal (posterior) root has a ganglion
• Ventral (anterior)
• Two roots merge laterally and form the spinal
  nerve

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Organization of Neurons in the Spinal Cord and
Spinal Nerves

• Dorsal root ganglion collections of cell bodies
  of unipolar sensory neurons forming dorsal roots.

• Motor neuron cell bodies are in anterior and
  lateral horns of spinal cord gray matter.
• Multipolar somatic motor neurons in anterior
  (motor) horn
• Autonomic neurons in lateral horn
• Axons of motor neurons form ventral roots and
  pass into spinal nerves

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Reflex Arc

• Basic functional unit of nervous system and
  simplest portion capable of receiving a stimulus
  and producing a response
• Automatic response to a stimulus that occurs
  without conscious thought. Homeostatic.

• Components
• Action potentials produced in sensory receptors
  transmitted to
• Sensory neuron. To-Interneurons. To-Motor neuron.
  To-
• Effector organ which responds with a reflex

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Structure of Peripheral Nerves

• Consist of
• Axon bundles
• Schwann cells
• Connective tissue
• Endoneurium surrounds individual neurons
• Perineurium surrounds axon groups to form
  fascicles
• Epineurium surrounds the entire nerve

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Branches of Spinal Nerves

• Dorsal Ramus innervate deep muscles of the trunk
  responsible for movements of the vertebral column
  and the C.T. and skin near the midline of the
  back.
• Ventral Ramus what they innervate depends upon
  which part of the spinal cord is considered.
• Thoracic region form intercostal nerves that
  innervate the intercostal muscles and the skin
  over the thorax
• Remaining spinal nerve ventral rami (roots of the
  plexus) form five plexuses (intermingling of
  nerves).

• Ventral rami of C1-C4 cervical plexus
• Ventral rami of C5-T1 brachial plexus
• Ventral rami of L1-L4 lumbar plexus
• Ventral rami of L4-S4 sacral plexus
• Ventral rami of S4 and S5 coccygeal plexus

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Brain and Cranial Nerves

• Chapter 13

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Brain and Cranial Nerves

• Brain
• Part of CNS contained in cranial cavity
• Control center for many of bodys functions
• Much like a complex computer but more
• Parts of the brain
• Brainstem connects spinal cord to brain
  integration of reflexes necessary for survival
• Cerebellum involved in control of locomotion,
  balance, posture
• Diencephalon thalamus, hypothalamus
• Cerebrum conscious thought, control
• Cranial nerves part of PNS arise directly from
  brain. Two pairs arise from cerebrum ten pairs
  arise from brainstem

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Sagittal Section of Brain
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Brainstem Medulla Oblongata

• Most inferior part
• Continuous with spinal cord has both ascending
  and descending nerve tracts
• Regulates heart rate, blood vessel diameter,
  respiration, swallowing, vomiting, hiccupping,
  coughing, and sneezing
• Brainstem Pons
• Superior to the medulla oblongata
• Sleep center
• Respiratory center coordinates with center in
  medulla

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Brainstem Midbrain

• Also called mesencephalon
• Small and superior to pons
• Tectum four nuclei that form mounds on dorsal
  surface of midbrain. Corpora quadrigemina
• Each separate part is a colliculus
• Two superior colliculi involved in visual
  reflexes receive information from inferior
  colliculi, eyes, skin, cerebrum
• Two inferior colliculi involved in hearing

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Reticular Formation

• Group of nuclei scattered throughout brainstem
• Controls cyclic activities such as sleep-wake
  cycle (maintains alertness)

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Cerebellum

• Attached to brainstem posterior to pons
• Cerebellar peduncles fiber tracts that
  communicate with other parts of brain
• Superior to midbrain
• Middle to pons
• Inferior to medulla oblongata
• Gray cortex and nuclei with white matter (tracts)
  between
• Cortex folded in ridges called folia white
  matter resembles a tree (arbor vitae)

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Cerebellar Functions

• Flocculonodular lobe balance and eye movements
• Vermis and medial portion of hemispheres
  posture, locomotion, fine motor coordination
  leading to smooth, flowing movements
• Lateral hemispheres, major portion works with
  cerebrum to plan, practice, learn complex
  movements

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Diencephalon

• Located between brainstem and cerebrum
• Components thalamus, subthalamus, epithalamus,
  hypothalamus

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Thalamus

• Two lateral portions connected by the
  intermediate mass
• Surrounded by third ventricle
• Sensory information from spinal cord synapses
  here before projecting to cerebrum
• Medial geniculate nucleus auditory information
• Lateral geniculate nucleus visual information
• Ventral posterior nucleus most other types
  sensory information

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Hypothalamus

• Most inferior portion of diencephalon
• Mammilary bodies bulges on ventralsurface
  olfactory reflexes and emotional responses to
  odors
• Infundibulum stalk extending from floor
  connects hypothalamus to posterior pituitary
  gland. Controls endocrine system.
• Receives input from viscera, taste receptors,
  nipples, external genitalia, prefrontal cortex
• Efferent fibers to brainstem, spinal cord
  (autonomic system), through infundibulum to
  posterior pituitary, and to cranial nerves
  controlling swallowing and shivering
• Important in regulation of mood, emotion,sexual
  pleasure, satiation, rage, and fear

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Cerebrum

• Largest portion of brain
• Composed of right and left hemispheres each of
  which has the following lobes frontal, parietal,
  occipital, temporal
• Sulci and Fissures
• Longitudinal fissure separates the two
  hemispheres
• Lateral fissure separates temporal lobe from
  frontal and parietal lobes
• Central sulcus separates frontal and parietal
  lobes
• Cortex outer surface
• Gyri are folds (increase surface area)
• Sulci are depressions

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Cerebrum, cont.

• Central sulcus between the precentral gyrus
  (primary motor cortex) and postcentral gyrus
  (primary somatic sensory cortex)
• Frontal lobe voluntary motor function,
  motivation, aggression, sense of smell, mood
• Parietal lobe reception and evaluation of
  sensory information except smell, hearing, and
  vision
• Occipital lobe reception and integration of
  visual input
• Temporal lobe reception and evaluation for smell
  and hearing memory, abstract thought, judgment.
  Insula is within.

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Meninges

• Connective tissue membranes
• Dura mater superficial
• Arachnoid mater
• Pia mater bound tightly to brain
• Spaces
• Subdural serous fluid
• Subarachnoid CSF

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Ventricles

• Lateral ventricles within cerebral
  hemispheres separated by
• septa pellucida
• Third ventricle within diencephalon
• Interventricular foramina join lateral
  ventricles with third

• Fourth ventricle associated with pons and
  medulla oblongata. Connected to third ventricle
  by the cerebral aqueduct, continuous with the
  spinal cord.

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Cerebrospinal Fluid (CSF)

• Similar to serum, but most protein removed
• Bathes brain and spinal cord
• Protective cushion around CNS
• Choroid plexuses produce CSF which fills
  ventricles and other parts of brain and spinal
  cord
• Composed of ependymal cells, their support
  tissue, and associated blood vessels
• Blood-cerebrospinal fluid barrier
• Endothelial cells of capillaries attached by
  tight junctions
• Substances do not pass between cells
• Substances must pass through cells
• Makes the barrier very selective

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Chapter 14

• Integration of
• Nervous System Functions

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Senses

• Means by which brain receives information about
  environment and body.
• Sensation (perception) conscious awareness of
  stimuli received by sensory receptors.
• Steps to sensation
• Stimuli originating either inside or outside of
  the body must be detected by sensory receptors
  and converted into action potentials, which are
  propagated to the CNS by nerves.
• Within the CNS, nerve tracts convey action
  potentials to the cerebral cortex and to other
  areas of the CNS.
• Action potentials reaching the cerebral cortex
  must be translated so the person can be aware of
  the stimulus.

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Types of Senses

• General distributed over large part of body.
  Receptor generates an action potential called a
  generator potential that then travels to the
  brain. Called primary receptors.
• Somatic (information about the body and
  environment) touch, pressure, temperature,
  proprioception, pain
• Visceral (information about internal organs)
  pain and pressure
• Special senses smell, taste, sight, hearing,
  balance.

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Types of Sensory Receptors

• Mechanoreceptors compression, bending,
  stretching of cells. Touch, pressure,
  proprioception, hearing, and balance
• Chemoreceptors chemicals become attached to
  receptors on their membranes. Smell and taste
• Thermoreceptors respond to changes in
  temperature
• Photoreceptors respond to light vision
• Nociceptors extreme mechanical, chemical, or
  thermal stimuli. Pain

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Types of Receptors Based on Location

• Exteroreceptors associated with skin
• Visceroreceptors associated with organs
• Proprioceptors associated with joints, tendons
  (proprioception is the sense of the
  orientation of one's limbs in space)

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Sensory Nerve Endings in Skin
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Free Nerve Endings

• Simplest, most common sensory receptor
• Scattered through most of body visceroceptors
  are of this type.
• Type responsible for temperature sensation
• Cold 10-15 times more numerous than warm
• Warm
• Pain responds to extreme cold or heat

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Merkel (Tactile) Disks

• Associated with dome-shaped mounds of thickened
  epidermis in hairy skin
• Light touch and superficial pressure

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Pacinian Corpuscles

• Deep cutaneous pressure vibration
• When associated with joints, involved in
  proprioception (proprioception is the sense of
  the orientation of one's limbs in space)

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Meissner (Tactile) Corpuscles

• Two-point discrimination
• Ability to detect simultaneous stimulations at
  two points on the skin.
• Used to determined texture of objects.
• Numerous and close together on tongue and
  fingertips
• Light touch light pressure

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Sensory and Association Areasof the Cerebral
Cortex

• Sensory
• Primary somatic sensory cortex (general sensory
  area) posterior to the central sulcus.
  Postcentral gyrus.
• General sensory input pain, pressure,
  temperature
• Taste area inferior end of postcentral gyrus
• Olfactory cortex inferior surface of frontal
  lobe
• Primary auditory cortex superior part of
  temporal lobe
• Visual cortex occipital lobe

• Association areas process of recognition
• Somatic sensory posterior to
• primary somatic sensory cortex
• Visual association anterior to
• visual cortex present visual
• information compared to past
• information

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Referred Pain

• Referred sensation in one region of body that is
  not source of stimulus. Organ pain usually
  referred to the skin. Both the organ and that
  region of the skin input to the same spinal
  segment and converge on the same ascending
  neurons.

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Phantom and Chronic Pain

• Phantom occurs in people who have appendage
  amputated or structure removed such as a tooth.
  Gate control theory of pain-- in uninjured limb,
  pressure and touch sensation inhibits pain (thus
  the success of massage in pain relief). These
  sensations are lost with amputations and thus
  their inhibitory effect.

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Control of Skeletal Muscles

• Motor system maintains posture and balance
  moves limbs, trunk, head, eyes facial
  expression, speech.
• Reflexes movements that occur without conscious
  thought
• Voluntary movements consciously activated to
  achieve a specific goal
• Two neurons upper and lower
• Upper motor neurons directly or through
  interneurons connect to lower
• Lower motor neurons axons leave the CNS, extend
  through PNS to skeletal muscles. Cell bodies in
  anterior horns of spinal cord and in cranial
  nerve nuclei of brainstem

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Motor Areas of the Cerebral Cortex

• Precentral gyrus (primary motor cortex, primary
  motor area) 30 of upper motor neurons. Another
  30 in premotor area. Control voluntary
  movements, especially fine motor movements of
  hands
• Premotor area anterior to primary motor cortex.
  Motor functions organized before initiation
• Prefrontal area motivation, foresight to plan
  and initiate movements, emotional behavior, mood

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Direct Pathways

• Control muscle tone and conscious fine, skilled
  movements in the face and distal limbs
• Direct synapse of upper motor neurons of cerebral
  cortex with lower motor neurons in brainstem or
  spinal cord
• Tracts
• Corticospinal direct control of movements below
  the head
• Corticobulbar direct control of movements in
  head and neck

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Indirect Pathways

• Control conscious and unconscious muscle
  movements in trunk and proximal limbs.
• Synapse in some intermediate nucleus rather than
  directly with lower motor neurons.
• Tracts
• Rubrospinal upper neurons synapse in red
  nucleus. Similar to comparator function of
  cerebellum. Regulates fine motor control of
  muscles in distal part of upper limb.
• Vestibulospinal influence neurons innervating
  extensor muscles in trunk and proximal portion of
  lower limbs help maintain upright posture.
• Reticulospinal maintenance of posture.

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Cerebellum

• Helps maintain muscle tone in postural muscles,
  helps control balance during movement, and
  coordinate eye movements

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Cerebellar Comparator Function

1. The motor cortex sends action potentials to lower
   motor neurons in the spinal cord.
2. Action potentials from the motor cortex inform
   the cerebellum of the intended movement.

• Lower motor neurons in the spinal cord send
  action potentials to skeletal muscles, causing
  them to contract.
• Proprioceptive signals from the skeletal muscles
  and joints to the cerebellum convey information
  cerebellum helps accomplish fine motor
  coordination of simple movements. It compares
  the intended movement with the actual movement
  and the result is smooth coordinated movements.
  (ex touching your nose--------not rapid complex
  movements)

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Speech

• Area normally in left cerebral cortex
• Wernicke's area sensory speech- understanding
  what is heard and thinking of what one will say.
• Broca's area motor speech- sending messages to
  the appropriate muscles to actually make the
  sounds.
• Sound is heard first in the 1o association area,
  then information travels to Wernicke's area.
  Neuronal connections between Wernicke's area and
  Broca's area.
• Aphasia absent or defective speech or language
  comprehension. Caused by lesion somewhere in the
  auditory/speech pathway.

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Right and Left Cerebral Cortex

• Right controls muscular activity in and receives
  sensory information from left side of body
• Left controls muscular activity in and receives
  sensory information from right side of body
• Sensory information of both hemispheres shared
  through commissures corpus callosum
• Language, and possibly other functions like
  artistic activities, not shared equally
• Left mathematics and speech
• Right three-dimensional or spatial perception,
  recognition of faces, musical ability

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Chapter 16

• Autonomic Nervous System

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Peripheral Nervous System

• Peripheral nerves contain both motor and sensory
  neurons
• Among the motor neurons, some of these are
  somatic and innervate skeletal muscles while some
  are autonomic and innervate smooth muscle,
  cardiac muscle, and glands
• Sensory neurons are not subdivided into somatic
  and autonomic since there is overlap in function
  e.g., pain receptors can stimulate both somatic
  and autonomic reflexes

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Somatic and Autonomic Nervous Systems

• Somatic
• Skeletal muscle
• Conscious and unconscious movement
• Skeletal muscle contracts
• One synapse
• Acetylcholine
• Receptor molecules nicotinic

• Autonomic
• Smooth and cardiac muscle and glands
• Unconscious regulation
• Target tissues stimulated or inhibited
• Two synapses
• Acetylcholine by preganglionic neurons and ACh or
  norepinephrine by postganglionic neurons
• Receptor molecules varies with synapse and
  neurotransmitter

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Autonomic Nervous System

• Divided into sympathetic and parasympathetic
  divisions as well as the enteric nervous system
• Sympathetic and parasympathetic divisions often
  supply the same organs but differ in a number of
  features
• The enteric nervous system
• Nerve plexuses within the wall of the digestive
  tract.
• Contributions from sensory neurons between
  digestive tract and CNS, ANS motor neurons
  between the CNS and the digestive tract, and
  enteric neurons confined within the plexuses
• Functions
• Stimulate/inhibit smooth muscle contraction
• Stimulate/inhibit gland secretions
• Detect changes in content of lumen
• Interneurons connect sensory and motor aspects of
  enteric

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Sympathetic (Thoracolumbar) Division

• Preganglionic cell bodies in lateral horns of
  spinal cord T1-L2 thoracolumbar
• Preganglionic axons pass through ventral roots to
  white rami communicantes to the retroperitoneal
  sympathetic chain ganglia.

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Routes of Sympathetic Axons

1. Spinal nerves preganglionic axons synapse (at
   the same or different level) with postganglionic
   neurons within the sympathetic chain. These
   postganglion neurons exit the ganglia through the
   gray rami communicantes and re-enter spinal
   nerves.
2. Sympathetic nerves preganglionic axons synapse
   (at the same or different level) with
   postganglionic neurons, which exit the ganglia
   through sympathetic nerves

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Routes of Sympathetic Axons

1. Splanchnic nerves preganglionic axons pass
   through the chain ganglia without synapsing to
   form splanchnic nerves. Preganglionic axons then
   synapse with postganglionic neurons in collateral
   ganglia. Postganglionic neurons then send fibers
   to target organs (viscera).
2. Innervation to adrenal gland preganglionic axons
   synapse with the cells of the adrenal medulla.
   Embryologically, adrenal medulla is derived from
   same cells as postganglionic ANS cells. Medullary
   cells secrete epinephrine and norepinephrine act
   as hormones promoting physical activity.

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Parasympathetic (Craniosacral) Division

• Preganglionic cell bodies in nuclei of brainstem
  or lateral parts of spinal cord gray matter from
  S2-S4
• Preganglionic axons from brain pass to terminal
  ganglia through cranial nerves III, VII, IX and X
• Preganglionic axons from sacral region pass
  through pelvic splanchnic nerves to terminal
  ganglia
• Terminal ganglia located near organ innervated or
  embedded in wall of organ

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Enteric Nervous System

• Consists of nerve plexuses within wall of
  digestive tract
• Sources of neurons
• Sensory neurons that connect the digestive tract
  to CNS
• ANS motor neurons that connect CNS to digestive
  tract
• Enteric neurons that are confined to enteric
  plexuses

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Parasympathetic Division

• Outflow is through cranial and pelvic splanchnic
  nerves
• Cranial nerves supplying the head and neck.
  Preganglion axons extend to terminal ganglia in
  head. Postganglionic neurons supply nearby
  structures.
• Oculomotor nerve through ciliary ganglion.
  Ciliary muscles and iris of the eye
• Facial nerve through pterygopalatine ganglion
  supplies lacrimal gland and mucosal glands of
  nasal cavity and palate. Through submandibular
  ganglion, supplies submandibular and sublingual
  salivary glands
• Glossopharyngeal nerve through otic ganglion
  supplies parotid salivary gland

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Sensory Neurons in Autonomic Nerve Plexuses

• Parts of reflex arcs regulating organ activities
• Transmit pain and pressure sensations from organs
  to the CNS

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Physiology of ANS

• Neurotransmitters primary substances produced by
  neurons of ANS
• Acetylcholine released by cholinergic neurons
• Norepinephrine released by adrenergic neurons
• Certain cells have receptors that combine with
  neurotransmitters causing a response in the cell
• Cholinergic bind acetylcholine. Have two
  different forms nicotinic and muscarinic
• Nicotinic all receptors on postganglionic
  neurons, all skeletal muscles, adrenal glands
• Muscarinic all receptors on parasympathetic
  effectors, receptors of some sweat glands
• Adrenergic receptors bind norepinephrine/epinephri
  ne
• Alpha and beta receptors.These are further
  subdivided into categories. a1 and ß1 usually
  have opposite affects than a2 and ß2

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Location of ANS Receptors
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Regulation of ANS

• Autonomic reflexes control most of activity of
  visceral organs, glands, and blood vessels.
• Autonomic reflex activity influenced by
  hypothalamus and higher brain centers, but it is
  the hypothalamus that has overall control of the
  ANS.
• Sympathetic and parasympathetic divisions
  influence activities of enteric nervous system
  through autonomic reflexes. These involve the
  CNS. But, the enteric nervous system can function
  independently of CNS through local reflexes.
  E.g., when wall of digestive tract is stretched,
  sensory neurons send information to enteric
  plexus and then motor responses sent to smooth
  muscle of gut wall and the muscle contracts.

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Autonomic Reflexes

1. Parasympathetic reflex via vagus lowers heart
   rate.
2. Sympathetic reflex via cardiac accelerator nerves
   (sympathetic) cause heart rate to increase.

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Enteric Nervous System Autonomic and Local
Reflexes

• Regulation of activity of digestive tract
• Sensory neurons of enteric plexuses supply CNS
  with information
• Autonomic neurons affect responses of smooth
  muscle and glands
• Local reflex does not involve CNS. Produces
  involuntary, unconscious, stereotypical response
  to stimulus. E.g., stretch of wall of digestive
  tract causes contraction of smooth muscle of the
  wall.

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Influence of Brain on Autonomic Functions
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Functional Generalizations of ANS

• Dual innervation to most organs with sympathetic
  and parasympathetic having the opposite effects.
• Either division alone or both working together
  can coordinate activities of different
  structures.
• Sympathetic prepares body for physical activity
  or flight-or-fight response. But also important
  at rest. Blood vessel walls receive only
  sympathetic stimulation, so at rest, sympathetic
  is responsible for maintenance of blood pressure.
• In general, parasympathetic more important for
  resting conditions SLUDD salivation,
  lacrimation, urination, digestion, defecation

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Innervation of Organs by ANS
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Responses to Exercise (Fight or Flight Response)

• Increased heart rate and force of contraction
• Blood vessel dilation in skeletal and cardiac
  muscles
• Dilation of air passageways
• Energy sources availability increased
• Glycogen to glucose
• Fat cells break down triglycerides
• Muscles generate heat, body temperature increases
• Sweat gland activity increases
• Decrease in nonessential organ activities