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Spinal Cord and Spinal Nerves


Chapter 12 Spinal Cord and Spinal Nerves 12-* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 16-* Autonomic Reflexes ... – PowerPoint PPT presentation

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Title: Spinal Cord and Spinal Nerves

Spinal Cord and Spinal Nerves
  • Chapter 12

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.

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

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

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.
  • Effector organ which responds with a reflex

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

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
  • 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
  • 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

Brain and Cranial Nerves
  • Chapter 13

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

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

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

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

  • 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)
  • Cortex folded in ridges called folia white
    matter resembles a tree (arbor vitae)

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

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

  • 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

  • Most inferior portion of diencephalon
  • Mammilary bodies bulges on ventralsurface
    olfactory reflexes and emotional responses to
  • 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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  • 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
  • Lateral fissure separates temporal lobe from
    frontal and parietal lobes
  • Central sulcus separates frontal and parietal
  • Cortex outer surface
  • Gyri are folds (increase surface area)
  • Sulci are depressions

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
  • Occipital lobe reception and integration of
    visual input
  • Temporal lobe reception and evaluation for smell
    and hearing memory, abstract thought, judgment.
    Insula is within.

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

  • 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.

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
  • 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

Chapter 14
  • Integration of
  • Nervous System Functions

  • 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.

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,

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
  • Photoreceptors respond to light vision
  • Nociceptors extreme mechanical, chemical, or
    thermal stimuli. Pain

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
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

Merkel (Tactile) Disks
  • Associated with dome-shaped mounds of thickened
    epidermis in hairy skin
  • Light touch and superficial pressure

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)

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
  • Light touch light pressure

Sensory and Association Areasof the Cerebral
  • Sensory
  • Primary somatic sensory cortex (general sensory
    area) posterior to the central sulcus.
    Postcentral gyrus.
  • General sensory input pain, pressure,
  • Taste area inferior end of postcentral gyrus
  • Olfactory cortex inferior surface of frontal
  • 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

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

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.

Control of Skeletal Muscles
  • Motor system maintains posture and balance
    moves limbs, trunk, head, eyes facial
    expression, speech.
  • Reflexes movements that occur without conscious
  • 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

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
  • Premotor area anterior to primary motor cortex.
    Motor functions organized before initiation
  • Prefrontal area motivation, foresight to plan
    and initiate movements, emotional behavior, mood

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

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.

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

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

  • 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
  • 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.

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

Chapter 16
  • Autonomic Nervous System

Peripheral Nervous System
  • Peripheral nerves contain both motor and sensory
  • 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

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

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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
  • The enteric nervous system
  • Nerve plexuses within the wall of the digestive
  • 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

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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.

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
  2. Sympathetic nerves preganglionic axons synapse
    (at the same or different level) with
    postganglionic neurons, which exit the ganglia
    through sympathetic nerves

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.

Parasympathetic (Craniosacral) Division
  • Preganglionic cell bodies in nuclei of brainstem
    or lateral parts of spinal cord gray matter from
  • 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
  • Terminal ganglia located near organ innervated or
    embedded in wall of organ

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
  • Enteric neurons that are confined to enteric

Parasympathetic Division
  • Outflow is through cranial and pelvic splanchnic
  • Cranial nerves supplying the head and neck.
    Preganglion axons extend to terminal ganglia in
    head. Postganglionic neurons supply nearby
  • 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

Sensory Neurons in Autonomic Nerve Plexuses
  • Parts of reflex arcs regulating organ activities
  • Transmit pain and pressure sensations from organs
    to the CNS

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
  • Alpha and beta receptors.These are further
    subdivided into categories. a1 and ß1 usually
    have opposite affects than a2 and ß2

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
  • 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.

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

Enteric Nervous System Autonomic and Local
  • 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

Influence of Brain on Autonomic Functions
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
  • 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

Innervation of Organs by ANS
Responses to Exercise (Fight or Flight Response)
  • Increased heart rate and force of contraction
  • Blood vessel dilation in skeletal and cardiac
  • 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
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