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Anatomy and function of the spinal cord and nerves

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Anatomy and function of the spinal cord and nerves Spinal cord Ch. 14, 17 Functions of ANS fight or flight (sympathetic) More widespread and longer lasting ... – PowerPoint PPT presentation

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Title: Anatomy and function of the spinal cord and nerves


1
Anatomy and function of the spinal cord and nerves
  • Spinal cord
  • Ch. 14, 17

2
Spinal cord is protected by vertebrae, meninges
and CSF
  • Canal formed by foramina of vertebrae
  • Meninges
  • Dura mater
  • Arachnoid mater
  • Pia mater
  • CSF formed in brain
  • Found in subarachnoid space

3
Anatomy of the spinal cord and spinal nerves
4
31 pairs of spinal nerves
  • 8 cervical
  • 12 thoracic
  • 5 lumbar
  • 5 sacral
  • 1 coccygeal
  • All are mixed nerves

5
Internal structure of spinal cord
  • Roots connect spinal nerves to spinal cord
  • Dorsal root- sensory neurons
  • Ganglion-cell bodies of sensory neurons
  • Ventral root- motor neurons
  • Horns- gray matter integrates sensory and motor
    information
  • Anterior, posterior, lateral
  • White matter- myelinated sensory and motor
    tracts
  • Columns- anterior, posterior, lateral

6
Regions of white and gray matter
  • Dorsal (posterior) horns- sensory neurons
  • Ventral (anterior) horns- motor neurons
  • Lateral horns- autonomic (motor) neurons
  • Columns- ascending (sensory) and descending
    (motor) tracts

7
Sensory and motor tracts
  • Named according to its position and pathway
  • Sensory impulses move up tracts and columns
  • Join the pool of sensory information
  • Voluntary motor output emanates from cerebral
    cortex (direct pathways)
  • Involuntary output originates in brain stem and
    hypothalamus (indirect pathways)

8
Spinal nerves
  • Comprise the peripheral nervous system (PNS)
  • Connect the CNS to muscles, sensory receptors and
    glands
  • 31 pairs of spinal nerves
  • Posterior and anterior roots (mixed nerves)

9
Distribution of spinal nerves
  • Branches (rami)
  • Posterior (muscles and surfaces anterior)
  • Meningeal branch (CNS)
  • Rami communicantes- autonomic system
  • Plexuses- network of axons
  • Cervical, brachial, lumbar, sacral

10
Map of spinal nerves
  • Motor fibers
  • Sensory fibers

11
Major plexuses example cervical plexus
  • Origin (C1- C5)
  • Superficial or deep
  • Superficial- skin mostly sensory
  • Deep-muscle largely motor
  • Severing spine above phrenic nerve causes
    respiratory arrest

12
More plexuses
  • Brachial
  • Shoulders, upper limbs
  • Axial, musculocutaneous, radial, medial, ulnar
  • Lumbar
  • Anterolateral abdominal wall, genitalia, part of
    lower limbs
  • Sacral and coccygeal
  • Buttocks, perineum, lower limbs
  • Damage can cause loss of sensation, palsy, loss
    of motor control
  • Intercostal nerves directly innervate muscles (no
    plexuses)

13
Dermatomes
  • Sensory neurons convey information form skin to
    CNS
  • Dermatomes- areas of skin that provide sensory
    input to a particular pair of nerves
  • Some overlap
  • Can be useful for diagnosis

14
Cervical plexus
15
Brachial plexus
16
Brachial plexus (C1-C8, T1)
17
Lumbar and sacral plexuses
18
Reflex arcs- fast involuntary responses to stimuli
19
Reflex arcs may be somatic or autonomic
  • Patellar reflex (knee-jerk)
  • Tap patellar ligament quadriceps femoris
    contracts
  • Achilles reflex (ankle-jerk)
  • Tap calcaneal tendon gastrocnemius and soleus
    muscles contract
  • Babinski sign- test for continuity of the
    corticospinal tract (goes from positive to
    negative with development)
  • Abdominal reflex
  • Can be useful for diagnosis of chronic disease or
    nerve damage

20
Types of reflexes
21
Autonomic vs. somatic nervous system
  • Somatic senses (pain, thermal, tactile,
    proprioreceptive)
  • Somatic motor neurons- skeletal muscle
  • Usually voluntary
  • Motor units
  • Acetylcholine
  • Autonomic sensory (chemoreceptors, mechano-
    (stretch) receptors
  • Motor neurons regulate visceral activities can
    function independently of ANS
  • Preganglionic and postganglionic neurons
  • Acetylcholine or norepinephrine

22
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23
Organization of ANS
24
Different types of ganglia
  • Sympathetic
  • Sympathetic trunk
  • Innervate organs above the diaphragm
  • Superior, middle, inferior cervical ganglia
  • Prevertebral
  • Below the diaphragm
  • Celiac, superior and inferior mesenteric ganglia
  • Parasympathetic
  • Preganglionic axons are longer than in
    sympathetic ganglia
  • Preganglionic neurons are myelinated,
    postganglionic neurons are not

25
Review of spinal nerve distribution
26
Sympathetic (thoracolumbar)
  • Sympathetic chain ganglia, paired
  • Head and thoracic cavity
  • Collateral ganglia, unpaired
  • Abdominopelvic cavity
  • Suprarenal medullae, paired
  • hormonal

27
Functions of the sympathetic division
  • Sympathetic chain ganglia
  • Diversion of blood flow to skeletal muscles and
    brain
  • Sweating pupil dilation
  • Collateral ganglia
  • Vasoconstriction restrict urinary function
  • Suprarenal medullae
  • Release of epinephrine and norepinephrine

28
Parasympathetic (craniosacral) division of ANS
29
Parasympathetic system
  • Ganglia are located near, or in, target organs
  • Effects are directed more toward specific target
    organs

30
Autonomic plexuses along major arteries
31
Regulation by dual innervation
  • Systems intersect in plexuses
  • Cardiac
  • Pulmonary
  • Esophageal
  • Celiac
  • Inferior mesenteric
  • Hypogastric

32
Postganglionic neurons
  • Sympathetic system
  • One presynaptic neuron can diverge into many
  • Many organs can be affected at once (divergent)
  • May extend to adrenal medullae
  • Parasympathetic system
  • Many presynaptic neurons can converge on a single
    effector
  • Effect can be localized to a single effector

33
Action by neurotransmitters in ANS
  • Acetylcholine (cholinergic neurons)
  • All preganglionic
  • Sympathetic postganglionic innervation of sweat
    glands
  • All parasympathetic postganglionic neurons
  • Nicotinic, muscarinic receptors
  • Norepinephrine (adrenergic)
  • a and ß receptors
  • Can be excitatory or inhibitory

34
Functions of ANS
  • fight or flight (sympathetic)
  • More widespread and longer lasting
  • Norepinephrine and epinephrine can act as
    hormones as well as neurotransmitters
  • rest and digest (parasympathetic)
  • Salivation, lacrimation, urination, digestion and
    defecation

35
Control of ANS
36
Control of autonomic functions
  • Reflexes
  • Blood pressure
  • Digestion
  • Defecation and urination
  • Control within brain
  • Brain stem (cardiovascular, swallowing ,
    digestion)
  • Spinal cord (elimination)
  • Control and integration center is hypothalamus

37
Sympathetic vs parasympathetic effects
  • Parasympathetic tends to be organ-specific
  • More reflexes
  • Sympathetic tends to be more holistic
  • Divergence
  • Hormonal distribution
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