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Anatomy and Physiology I

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Presentation on theme: "Anatomy and Physiology I"— Presentation transcript:

1 Anatomy and Physiology I
Chapter 13 The Spinal Cord, Spinal Nerves, and Somatic Reflexes

2 Spinal Cord Functions Conduction Locomotion Reflexes
Bundles of nerve fibers conduct info up and down the cord Sensory info reaches brain Motor commands reach the effectors Locomotion Walking Central pattern generators- produce sequence of walking Reflexes Involuntary, stereotyped responses to stimuli

3 Spinal Cord Cylinder of nervous tissue Arises from brainstem L1
31 pairs of spinal nerves Divided into cervical, thoracic, lumbar, and sacral regions

4 The Meninges 3 fibrous connective tissue membranes Dura mater
Forms loose sleeve- dura sheath Epidural space- between vertebrae and sheath Arachnoid mater Loose mesh of fibers Subarachnoid space- between arachnoid membrane and pia mater Filled with CSF Pia mater Delicate membrane Follows contours of spinal cord

5 Spinal Cord Consists of 2 kinds of nervous tissue Gray matter
Dull color Little myelin White matter Bright, pearly white Abundance of myelin Surrounds gray matter Composed of tracts Carry signals from one part of the CNS to another

6 Gray Matter Central core- butterfly, H shaped 2 dorsal horns
2 ventral horns Gray commissure- connects R and L side Central canal

7 Gray Matter Branches into ventral and dorsal roots
Dorsal root- carries sensory nerve fibers to the spinal cord Enter posterior horn Ventral root- motor nerve fibers exit and go to skeletal muscles

8 Spinal Tracts Ascending tracts Descending tracts
carry sensory information up the spinal cord to the brain Descending tracts conduct motor impulses down the brain stem and the spinal cord Muscles or organs Tracts cross- decussation

9 Spinal Nerves Spinal cord communicates with body Nerve
Composed of numerous nerve fibers (axons) bound together by connective tissue PNS nerve fibers enclosed by Schwann cells

10 Spinal Nerves Endoneurium- thin layer of connective tissue
surrounds nerve fiber Fascicles- bundles of nerve fibers Perineurium- sheath surrounds fascicle Epineurium- surrounds several bundles of fascicles Whole nerve Protects nerve

11 Peripheral Nerve Fibers
Sensory fibers- afferent fibers Signals from sensory receptors to CNS Motor fibers- efferent fibers Signals from CNS to muscles and glands

12 Spinal Nerves Sensory nerves- afferent fibers
Motor nerves- efferent fibers Mixed nerve- both afferent and efferent fibers Conducts signals in 2 directions Ganglion (knot)- cluster of neurosomas outside the CNS

13 Spinal Nerves 31 pairs 8 cervical 12 thoracic 5 lumbar 5 sacral
1 coccygeal

14 Nerve Plexus Nerves merge to form web-like nerve plexus
Cervical plexus Brachial plexus Lumbar plexus Sacral plexus and Coccygeal plexus

15 Dermatomes Specific area of the skin the sends sensory information to the spinal cord Spinal nerves overlap Need to severe 3 successive spinal nerves to lose sensation in one dermatome area Spinal nerve damage assessed with pin pricks

16 Reflexes Quick, involuntary, stereotyped reactions of glands or muscles to stimulation 1. Require stimulation- not spontaneous reactions 2. Quick- minimum synaptic delay 3. Involuntary- difficult to suppress Occur w/out intent and awareness 4. Stereotyped- same way every time

17 Somatic Reflex Involuntary contraction of skeletal muscle
Employs a reflex arc- signal travels along a pathway 1. Somatic receptors Skin, muscle, tendon 2. Afferent nerve fibers Carry info into dorsal horn of spinal cord 3.Integrating center interneurons 4. Efferent nerves Carry info from ventral horn out to the skeletal muscle 5. Skeletal muscles Effectors that carry out response

18 Muscle Spindle Stretch receptors imbedded in skeletal muscle
Proprioceptors- sense organs specialized to monitor body position and movement of body parts Function: inform brain of muscle length and movement Brain sends motor commands back to muscles

19 The Stretch Reflex When muscle is stretched
“fights back” Contracts Feels stiffer This helps maintain equilibrium and posture Extension creates stretch reflex in flexors Flexion creates stretch reflex in extensors Stretch reflexes stabilize joints and coordinate vigorous and precise movements

20 The Tendon Reflex Reflexive contraction of muscle when tendon is tapped Depends on Reciprocal inhibition Prevents muscles from working against each other- inhibits antagonist

21 The Withdrawal (Flexor) Reflex
Quick contraction of flexor muscles resulting in the withdrawal of a limb from an injurious stimulus Contraction of flexors and relaxation of extensors

22 The Crossed Extension Reflex
Contraction of extensor muscles in the limp opposite from the one withdrawn Maintains balance, prevents falling Shift in center of gravity

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