Lab 8 Sensory and Reflex Physiology and the Spinal Cord

sensory receptor

specialized cell that transmits signals to sensory neurons

modality gated channel

opens in response to a stimulus other than a neurotransmitter or a voltage change at the plasma membrane

sensory modalities

Different forms of sensation (e.g., touch, pain, pressure, heat, cold, vision, taste, hearing, and smell)

receptive field

the region of the sensory surface that, when stimulated, causes a change in the firing rate of that neuron; •Smaller fields allow more precise stimulus localization

sensation

stimulus we are consciously aware of

sensory adaptation

•decreased awareness continuous stimulus due to decrease in frequency of action potentials despite stimulus

•ex. no longer smelling a certain smell in an area

tonic receptor

a receptor in which the frequency of action potentials declines slowly or not at all as stimulation is maintained; limited adaptation - respond continuously ex. proprioceptors and nociceptors (pain receptors)

phasic receptor

a receptor in which the frequency of action potentials drops rapidly as stimulation is maintained; adapts rapidly - will only respond to new stimuli; ex. mechanoreceptors

sensory homunculus

Demonstrates that the area of the cortex dedicated to the sensations of various body parts is proportional to how sensitive that part of the body is

reflex

rapid, preprogrammed, involuntary responses of muscles or glands to a stimulus

•A stimulus is required to initiate

•Response is rapid; involves a chain of only a few neurons

•The response is preprogrammed; always the same

•The response is involuntary; no intent or awareness before it happens

•A survival mechanism - we respond to a potentially detrimental stimulus immediately and awareness comes later

reflex arc

sensory receptor → sensory neuron → (interneuron), motor neuron → effector

spinal cord

a major part of the central nervous system which conducts sensory and motor nerve impulses to and from the brain; housed within the vertebral canal

nerve

bundle of axons in PNS

spinal nerves

31 pairs of nerves arising from the spinal cord; letter abbreviation for region of spine they originate from; forms where the anterior and posterior roots join; mixed nerves (contain sensory and motor fibers)

posterior (dorsal) rootlets

merge to form a root

posterior (dorsal) root

contains sensory axons

posterior (dorsal) root ganglion

contains cell bodies of sensory neurons

true spinal nerve

anterior root

contains motor axons

ramus

points where the spinal nerve branches; occurs away from the spinal cord

posterior (dorsal) ramus

innervates the muscles and joints in that region of the spine and the skin of the back

anterior (ventral) ramus

•Splits into multiple other branches

•At different levels, this ramus innervates anterior and lateral trunk, upper limb, lower limb

•Participates in plexuses

cervical region of spinal cord

supplies neck, shoulders, and upper limbs, C1-8

thoracic region of spinal cord

supplies thoracic cage, T1-12

lumbar region of spinal cord

supplies hips & front of lower limbs, L1-5

sacral region of spinal cord

supplies buttock, genitalia, and backs of lower limbs, S1-5

conus medullaris

inferior tapered end of spinal cord

cauda equina

collection of spinal nerves below the end of the spinal cord; below L1 vertebrae

filum terminale

fibrous extension of the pia mater; anchors the spinal cord to the coccyx

spinal meninges

dura mater, arachnoid mater, pia mater (PAD to protect the spinal cord from deep to superficial)

dura mater

thick, outermost layer of the meninges; 5 on image

arachnoid mater

middle weblike layer of the meninges; 4 on image

pia mater

thin, delicate inner membrane of the meninges; 3 on image

central canal of spinal cord

center of spinal cord which contains cerebrospinal fluid

posterior median sulcus

a shallow vertical groove dividing the spinal cord throughout its whole length in the midline posteriorly.

anterior median fissure

a groove along the anterior midline of the spinal cord that incompletely divides it into symmetrical halves

gray matter of the spinal cord

cell bodies, dendrites, and unmyelinated axons arranges in a butterfly shape with anterior and posterior "horns"

posterior (dorsal) horns

contain axons of sensory neurons and cell bodies (sensory nuclei) of interneurons

lateral horns

(only in thoracic and superior lumbar regions) - cell bodies of autonomic motor neurons

anterior (ventral) horn

cell bodies (motor nuclei) of somatic motor neurons

white matter of spinal cord

This area surrounds the gray matter. It is composed of both myelinated and unmyelinated axons. It has three regions, anterior, lateral, and posterior columns.

posterior (dorsal) funiculus

lies between the posterior gray horns on the posterior side of the cord and the posterior median sulcus; contains sensory tracts

lateral funiculus

white matter region on each lateral side of the spinal cord; contain sensory and motor tracts

anterior (ventral) funiculus

•Sits between anterior gray horns and anterior median fissure

•Left and right anterior funiculi are interconnected by white commissure

•Contains sensory (ascending) and motor (descending) tracts