A&P II - Chapter 14

Functions of the Spinal Cord and Spinal Nerves

1. structural and functional link between the brain and body

2. spinal reflexes

Conus Medullaris

inferior tapered end of the spinal cord

Posterior Median Sulcus

longitudinal depression of the spinal cord

Anterior Median Fissure

longitudinal depression of the spinal cord

cerival enlargement

widened region of the spinal cord housing neurons innervating upper limbs

lumbar enlargement

widened region of the spinal cord housing neurons innervating lower limbs

how many pairs of spinal nerves

posterior root contains

sensory neurons

posterior root ganglion contains

cell bodies of sensory neurons

anterior root contains

motor neurons

spinal nerves are classified as _____ nerves.

mixed

Cauda Equina

roots of lumbar, sacral, and coccygeal spinal nerves that extend inferiorly past the end of the spinal cord (conus medullaris)

typical adult spinal cord length

typical adult spinal cord diameter

3 things protecting spinal cord

1. bone (vertebral column)

2. meninges

3. cerebrospinal fluid (CSF)

spinal cord passes through the

vertebral canal

spinal nerves exit through

interverterbral foramen

pia mater

delicate layer of elastic and collagen fibers adhereing to spinal cord

denticulate ligaments

lateral extensions of piamater that help suspend the spinal cord

filum terminale

pia mater achchoring inferior end of spinal cord to coccyx

arachnoid mater

web-like layer just external to piamater

arachnoid trabeculae

fibrous extensions of arachnoid mater

subarachnoid space

area deep to arachnoid through which CSF flows

Dura Mater

tough outermost layer of dense irregular CT, stabilizes spinal cords

subdural space

area between dura and arachnoid mater

epidural space

area between dura and vertebrae

what is found in the epidural space

• adipose tissue

• areolar CT

• BVs

Spinal Cord Meninges

• pia mater

• arachnoid mater

• dura mater

Gray Matter is composed of

• neuron’s cell bodies

• dendrites

• unmyelinated axons

• glial cells

Posterior Horns

projections of grey matter from center of spinal cord; house axons of sensory neurons and cell bodies of interneurons

Anterior Horns

projections of gray matter from center of spinal cord; houses cell bodies of somatic motor neurons

Lateral Horns

projections of gray matter from center of spinal cord; houses cell bodies of autonomic motor neurons

Lateral Horns are only present

T1-L2

Gray Commissure

horizontal band of gray matter surrounding central canal of spinal cord

what is in the gray commissure

unmyelinated axons which connect L and R gray matter

Sensory Nuclei

group of cell bodies in the posterior horn that contain interneurons

Somatic Sensory Nuclei

receives signals from skin, muscle, and joints

Visceral Sensory Nuclei

receives signals from blood vessels and vicera

Motor Nuclei

group of motor neuron cell bodies in anterior and lateral horns of spinal cord

Somatic Motor Nuclei

in anterior horn, innervates skeletal muscle

Autonomic motor nuclei

in lateral horn, innervates smooth muscle, Cardiac muscle, and glands

Regions of White Matter in Spinal Cord

• posterior funiculus

• lateral funiculus

• anterior funiculus

Posterior Funiculus Location

between posterior gray horns and posterior median sulcus

Posterior Funiculus

contains sensory tracts, axon bundles called fasciculi

Lateral Funiculus

contains sensory (ascending) and motor (descending) tracts

Anterior Funiculus Location

between anterior gray horns and anterior median fissure

Anterior Funiculus

contains sensory (ascending) and motor (descending) tracts

White Commissure

interconnects L and R anterior funiculi

direction of sensory pathways

ascend toward brain

direction of motor pathways

descend away from brain

Spinal Pathway Characteristics

• paired L and R

• chain of two or more neurons

Decussate

axons cross midline

contralateral

brain processes information from opposite side of body

ipsilateral

brain processes information from same side of body

Sensory input transmitted through the spinal cord originates from

general sense receptors

Tactile Receptor

type of somatosensory receptor that detects characteristics of an object

proprioceptors

type of somatosensoryreceptor that detects stretch in joints, muscles, and tendons

viceral sensory receptors

detect changes in an organ

somatosensory pathways carry

signals from skin, muscles, and joints

viscerosensory pathways carry

signals from the viscera

Primary/ 1st Order Neuron

peripeheral ending, cell body in post. root ganglion, axon leading to secondary neuron

Secondary/2nd order Neuron

interneuron that received primary input, extends to to tertiary neuron ot cerebellum

Tertiary/3rd Order Neuron

interneuron that receives secondary input, extends to somatosensory cortex of parietal lobe of cerebrum

Posterior Funiculus - Medial Lemniscal Pathway

sensory input about discriminative touch and consious perception from proprioceptors

Primary Neuron of Medial Lemniscal Pathway

relays signal from skin to brainstem/medulla

Secondary Neuron of Medial Lemniscal Pathway

relays signal from medulla to thalamus

Tertiary Neuron of Medial Lemniscal Pathway

relays signal in thalamus to primary somatosensory cortex (postcentral gyrus)

Anterolateral Pathway

signals related to crude touch, pressure, pain, and temperature

Primary Neuron of Anterolateral Pathway

relays signal from skin to spinal cord

seconday neuron of anterolateral pathway

relays signal from spinal cord to thalamus

tertairy neuron of anterolateral pathway

relays signal from thalamus to cerebral cortex

Spinocerebellar Pathway

signals about proprioception with a two neuron chain

primary neuron of the spinocerebellar pathway

relays signal from skin to spinal cord

secondary neuron of the spinocerebellar pathway

relays signal from spinal cord to cerebellum

tertiary neuron of spinocerebellar pathway

does not exist

Motor Pathways

• control effectors, such as skeletal muscles

• start in brain and include at least two neurons

upper motor neuron

in motor cortex, cerebral nucleus or brainstem nucleus; contacts lower motor neuron

lower motor neuron

in cranial nerve nucleus or spinal cord anterior horn; excites muscle

Direct/Pyramidal Pathway

pathway between brain and skeletal muscles; begins with upper motor neurons in primary motor cortex, axons course through internals capsule, cerebral peduncles, and corticospinal tracts. Synapses with lower motor neuron in anterior horn of gray matter, lower motor neuron extends to skeletal muscle

Lateral Corticospinal Tracts

part of direct/pyramidal pathway

• upper motor neuron axons decussate within medulla’s pyramids

• axons form white tracts in lateral funiculi and contact lower motor neurons

• lower motor neurons innervate limb muscles for skilled movements

Anterior Corticospinal Tracts

part of direct/pyramidal pathway

• upper motor neuron axons form white tracts in anterior funiculi

• decussate at level of spinal cord segment and contact interneurons or lower motor neurons

• lower motor neurons innervate axial skeletal muscle

Indirect Pathway

upper motor neurons originate in brain stem nuclei and take complicated route to spinal cord

Lateral Pathway

• regulates precise movement and tone in flexor limb muscles

• consists of rubrospinal tracts originating in midbrain

Medial Pathway

• regulates muscle tone and movements of head, neck, proximal limb, and trunk

• consists of reticulospinal, tectospinal, and vestibulospinal tracts

reticulospinal tracts

• from reticular formation

• helps control reflexes related to posture and balance

Tectospinal Tracts

• from superior and inferior colliculi

  • regulate reflexive orienting responses to sicual and auditory stimuli

Vestibulospinal Tracts

• from vestibular nuclei of brainstem

• help maintain balance during sitting, standing, and walking

Posterior/Dorsal Ramus

small branch that innervated muscles and skin of back

Anterior/Ventral Ramus

larger branch that splits into multiple other brancehs, plexuses

Rami Communicantes

small branches of autonomic fibers that extend between spinal nerve and sympathetic trunk ganglion

Dermatomes

segment of skin supplied by a single spinal nerve, some overlap in innervated regions

Nerve Plexus

network on interweaving anterior rami of spinal nerves

4 main plexuses

• cervical

• brachial

• lumbar

• sacral

Intercostal Nerves

located between ribs, from anterior rami of T1-T11

T12

subcostal nerve

T1 anterior ramus

brachial plexus and innervates 1st intercostal space

T2 anterior ramus

innervated 2nd intercostal space and recives sensory information from axilla and medial arm surface

T3-T6 anterior rami

innervate intercostal muscles and recives sensory signals from ant. and lat. chest wall

T7-T12 anterior rami

innervate intercostal and abdominal muscles and recieve sensory information from overlying skin

Cervical Plexuses

• ant. rami of C1-C4 (C5 contributes a little)

• innervates ant. neck muscles, skin of neck, and portions of head/shoulders