Chapter 13 - Spinal cord & spinal nerves

Question 1

Protective structures:

Vertebral column and the **meninges (3) **(protective CT layer) provide protect the spinal cord and provide physical stability.

Answer 1

**1) dura mater - **superficial, continuous with brain dura mater, epineurium (outer layer of cranial/spinal nerve)

SUBDURAL SPACE

**2) arachnoid mater - **spiderweb arrangement

SUBARACHNOID SPACE

**3) pia mater - **deep, adheres to surface of CNS, **denticulate ligament **suspend spinal cord in middle of its dural sheath

Question 2

**External anatomy of spinal cord **

(2) enlargements

1) conus medullaris

**2) filum terminale **

Answer 2

**cervical & lumbar **enlargement

inferior to **lumbar enlargement, **spinal cord terminates at tapering **conus medullaris **

extension of pia mater extending inferiorly & fuses to arachnoid & dura mater - **filum terminale **anchors spinal cord to coccyx

Question 3

External anatomy of Spinal cord

Posterior (dorsal) root & anterior(ventral) root

Posterior (dorsal root) ganglion

cauda equina

Answer 3

**roots **= 2 bundles of axons that connect each spinal nerve to segment of cord by **rootlets **

**posterior (dorsal) root - only sensory axons, has swelling that contains sensory neuron cell bodies (posterior ganglion) **

**anterior (ventral) root **- only motor axons

**cauda equina - **roots of lumbar, sacral & coccygeal regions that run alongside **filum terminale **like wisps of hair

Question 4

Internal Anatomy of Spinal Cord

1) anterior median fissure
2) posterior median sulcuss
3) gray & white commissures
4) central canal
5) anterior, posterior & lateral gray horns
6) anterior, posterior & lateral white columns

Answer 4

1) wide groove on anterior side
2) narrow furrow on posterior side
3) gray- forms crossbar of H, white- connects white matter of left & right sides
4) space in center of gray commissure filled with CSF
5) gray matter subdivided into horns
6) white matter divided into columns - contains bundles of axons with common destination (tracts) - sensory = ascending, motor = descending

Question 5

White Matter

Gray Matter

Answer 5

**White - **bundles of myelinated axons

**Gray - **neuronal cell bodies & dendrites, unmyelinated axons & neuroglia

Question 6

Nuclei

Answer 6

functional clusters of neuronal cell bodies in gray matter

Question 7

Spinal Nerve - 31 pairs; mixed nervs

Answer 7

Cervical (8)

Thoracic (12)

Lumbar (5)

Sacral (5)

Coccygeal (1)

Question 8

Connective tissue covering of spinal nervs (3)

define: fiber, fascicle & nerve

Answer 8

**1) endoneurium - **wraps individual axons within nerve

**2) perineurium - **wraps fascicles

**3) epineurium - **wraps around entire nerve

**fiber - **single axon within endoneurium

**fascicle - **bundle of fibers within perineurium

**nerve - **bundle of fascicles with epineurium

Question 9

Rami of Spinal Nerves

Answer 9

spinal nerve branches

Question 10

**Rami **of Spinal Nerves (2)

Answer 10

**posterior (dorsal) ramus - **serve deep muscles & posterior skin of trunk

**anterior (ventral) ramus - **muscles/structures of limbs & skin of lateral & anterior trunk

Question 11

**All anterior rami **form **plexuses **except?

Answer 11

T1-T11

Question 12

Cervical Plexus

Answer 12

formed by **anterior rami of C1-C5 **

superficial & deep branches

phrenic nerve - important (diaphragm)

Question 13

Brachial plexus

Answer 13

formed by anterior rami of C5-C8 & T1

supplies shoulders & upper limbs

Question 14

Brachial Plexus:

roots (unite)→ __..?

Answer 14

roots (unite)→ **trunk (superior/middle/inferior) → **divisions(anterior/posterior)→ cord(lateral/medial/posterior)**→ nerves **

Question 15

Important nerves that arise from **brachial plexus **(5)

Answer 15

axillary

musculocutaneous

radial

median

ulnar

Question 16

Lumbar Plexus

Answer 16

formed by** anterior rami of L1-L4**

supplies anterolateral abdominal wall, external genitals, and part of lower limbs.

**Femoral & Obturator Nerves **

Question 17

Sacral Plexus

Answer 17

anterior rami of L4-L5 and S1-S4

supplies butt, perineum & lower limbs

gives rise to large nerve in body - SCIATIC nerve

Question 18

Coccygeal Plexus

Answer 18

Formed by anterior rami of S4-S5 and **coccygeal nerves. **

supplies small area of skin in coccygeal region

Question 19

Dermatome

Answer 19

the area of the skin that provides sensory input to CNS via 1 pair of spinal nerves or trigeminal nerve

Question 20

Sensory and Motor Tracts

White matter tracts & gray matter

Answer 20

**White Matter Tracts - **highways for nerve impulse propogation

**Gray matter - **recieves & integrates incoming & outgoing info

Question 21

Reflex

Answer 21

fast, involuntary. unplanned response to a stimulus

Question 22

Reflex Arc

Answer 22

pathway followed by nerve impulses that produce a reflex

Question 23

A reflex arc includes (5)?

Answer 23

**1) sensory receptor **- responds to stimulus

**2) sensory neuron - **nerve impulse propogates to axon terminals in gray matter -> relay neurons to brain

**3) integrating center **

4) motor neuron

6) effector

Question 24

The Stretch Reflex

Answer 24

feedback mechanism to control muscle LENGTH

Causes contraction of skeletal muscle in response to stretching of muscle.

monosynaptic

**ipsilateral - **same side

**ex) knee jerk: **stretching → activation of muscle spindles → sensory neuron →spinal cord →motor neuron → muscle contraction

Question 25

Tendon Reflex

Answer 25

feedback mechanism to control muscle **tension **by causing relaxation **polysynaptic ** sensory receptor = **golgi tendon organs** tension applied to tendon → tendon organ stimulated →nerve impulse →spinal cord →motor neuron → muscle relaxation to relieve tension

Question 26

Flexor (withdrawal) Reflex

Answer 26

Stepping on a tack (**stimulus**) → nerve impulse → activation of **interneuron** → activation of **motor** neuron →muscle **contraction **→**withdrawal** of the leg. **polysynaptic ** **ipsilateral **

Question 27

Crossed Extensor Reflex

Answer 27

**polysynaptic ** **contralateral** Contraction of muscles that extend joints in opposite limb in response to a painful stimulus. Stepping on a tack (**stimulus**) → **nerve impulse**→activation of several **interneurons** → **motor** neurons → muscle **contraction→ **flexion of leg stepping on a tack & extension on opposite side. **for maintaining balance**