Title: Anatomy and function of the spinal cord and nerves
1Anatomy and function of the spinal cord and nerves
- Spinal cord
- Autonomic nervous system
- Ch. 18, 20
2Spinal 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
3Anatomy of the spinal cord and spinal nerves
4Internal 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
5Regions 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
6Sensory 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 form cerebral
cortex (direct pathways) - Involuntary output originates in brain stem and
hypothalamus (indirect pathways)
7Reflex arcs- fast involuntary responses to stimuli
8Reflex 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
9Spinal 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)
10Distribution 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
11Major plexuses pp. 566-576example cervical
plexus
- Origin (C1- C5)
- Superficial or deep
- Superficial- skin mostly sensory
- Deep-muscle largely motor
- Severing spine above phrenic nerve causes
respiratory arrest
12More 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)
13Dermatomes
- 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
14Autonomic 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
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16Different 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
17Sympathetic (thoracolumbar)
18Parasympathetic (craniosacral)
19Autonomic plexuses along major arteries
20Postganglionic neurons
- Sympathetic system
- One presynaptic neuron can diverge into many
- Many organs can be affected at once
- May extend to adrenal medullae
- Parasympathetic system
- Many presynaptic neurons can converge on a single
effector - Effect can be localized to a single effector
21Action 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
22Functions 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 - See pp. 644-645
23Control 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