Anatomy & Physiology RAT 20

What two roots attach a spinal nerve to the spinal cord?

anterior and posterior root containing sensory and motor fibers

How long is a spinal nerve?

1-2 cm

What are the names of the two large branches of the spinal nerve?

posterior and anterior ramus

Is the posterior ramus sensory, motor, or mixed?

mixed, travels to the posterior side of the body

Is the anterior ramus sensory, motor, or mixed?

mixed, travel to the anterior side of the body

Ramus Communicantes

small branch that contains autonomic fibers

How many pairs of spinal nerves are there?

31 pairs

Nerve Plexus

complicated networks of nerves where the anterior rami of the cervical, lumbar, and sacral spinal nerves merge

Which branches form a plexus?

cervical, lumbar, sacral

Where is the cervical plexus located?

from C1-C4, small contribution from C5 and the hypoglossal nerve (XII)

What major nerve arises from the cervical plexus?

phrenic nerve that innervates the diaphragm

Where is the brachial plexus located?

from C5-T1

Axillary Nerve

C5-C6, branch of the posterior cord; motor to the deltoid and teres minor muscles, sensory to the skin over the deltoid

Radial Nerve

C5-T1, continuation of the posterior cord; motor to the triceps brachii, brachioradialis, and the extensor muscles of the forearm and digits, sensory to the posterior arm and forearm, posterior thumb, and posterior second, third, and lateral galf of the fourth digits

Musculocutaneous Nerve

C5-C6, continuation of the lateral cord; motor to the biceps brachii, coracobrachialis, and brachialis muscles, sensory to the lateral forearm

Median Nerve

C5-T1, from the fusion of the medial and lateral curve; motor to most of the muscles that flex the wrist and digits and certain muscles of the hand, sensory to the anterior thumb and the anterior second, third, and lateral side of the fourth digits

Do the anterior rami of thoracic nerves form a plexus?

no

Intercostal Nerve

the nerves that form from anterior rami

Where is the lumbar plexus located?

from L1-L4

What is the name of the largest nerve that arises from the lumbar plexus?

femoral nerve

Where is the sacral plexus located?

from L4-S4

What is the name of the largest nerve that arises from the sacral plexus?

sciatic nerve

What is the largest and longest nerve in the body?

SCIATIC NERVE

Basic Pathway for Sensory Information

(1) stimulus is detected by sensory receptors of the PNS, (2) transmitted by PNS sensory neurons to the CNS, (3) integrated by CNS neurons

Sensory Transduction

the conversion of a sensory stimulus to an electrical signal

Where does sensory transduction take place?

begins at a sensory receptor

Types of Sensory Receptors

encapsulated nerve endings and free nerve endings

How does pressure lead to an action potential in a somatic sensory neuron?

(1) before any stimulus arrives, the ion channels in the axolemma of the somatic sensory neuron are closed, (2) when a stimulus such as pressure is applied, mechanically gated sodium ion channels open and sodium ions enter the axoplasm, generating a temporary depolarization referred to as receptor potential, (3) if enough Na+ enter to reach threshold, voltage-gated ion channels open and trigger an action potential

Adaptation

some receptors respond rapidly and with high intensity but stop sending the stimuli after a certain period

Which type of receptors will stop sending a signal even though the stimulus is still present?

rapid adapting receptors

Which type of receptors continue to send a signal?

slowly adapting receptors

Exteroceptors

receptors that detect stimuli originating outside the body; ex. texture, temperature, color, light

Interoceptors

receptors that detect stimuli originating inside the body; ex. blood pressure, organ stretch

Categories of Receptors

mechanoreceptors, thermoreceptors, chemoreceptors, photoreceptors, nocicepter

Proprioceptors

a sensory receptor that responds to a change in position of a body part, particularly a ligament or tendon

Most sensory neurons are what type of neuron?

pseudounipolar neuron

Where are the cell bodies of sensory neurons located?

in a posterior root ganglion

What is the peripheral process of a sensory neuron?

a long axon

What is the central process of a sensory neuron

exits the cell and travels to the posterior horn

What two factors determine the speed of transduction of axons?

axon diameter and thickness of its myelin sheath

Is proprioceptive information transmitted quickly or slowly?

quickly

What type of axons would you expect to find on proprioceptors?

large axons with a thick myelin sheath

Is temperature and pain information transmitted quickly or slowly?

slowly

What type of axons would you expect to find on thermoreceptors and nociceptors?

small axons with thin myelin sheaths

Which area contains more sensory neurons, the fingertips or the forearm?

fingertips

Which has a larger sensory field, the fingertips or the forearm?

the forearm

Two-Point Discrimination

two stimuli are moved apart until the subject can feel two distinct points

A dermatome is a segment of _________. Each dermatome is determined by the _____________ that serves it.

skin; spinal nerve

Layers of the Retina

outer pigmented epithelium and inner layer

Types of Photoreceptors

adjacent to the pigmented layer- rods and cones

What cells synapse with the photoreceptors?

bipolar cells

What cells follow bipolar cells in the pathway?

retinal ganglion cells, axons form the optic nerve

What layers does the light have to pass through before encountering the photoreceptors?

retinal ganglion cells and bipolar cells

Cones

detect color, function best in bright light, highest concentration in the fovea centralis, the edge lacks cones, responsible for high acuity (sharp) vision

Rods

detect black and white, function best in dim light, fovea centralis lacks rods, responsible for peripheral visioin

Basic Parts of a Rod & Cone

synaptic terminals, cell bodies with nuclei, inner segments with organelles, outer segment

What is found in the outer segment?

discs

What pigment is found in the disc membrane of a rod?

rhodopsin

What are the two components of rhodopsin?

opsin protein and the retinal pigment

How many types of cone pigments are there?

blue, red, and green

Color Blindness

defective gene for one or more cone pigments

Most Common Form of Color-Blindness

red-green color blindness

Why is color-blindness more common in men?

it's a sex-linked disorder

How is the visual system fundamentally different than the other special senses?

hyperpolarization from light and reduces the release of neurotransmitters

How does the number of photoreceptors compare to the number of ganglion cells?

105 million to 1

Why is vision sharp in the fovea?

has a high concentration of cones

Why is peripheral vision less detailed?

there's no cones on the outer edge of the retina

Visual Field

the area one can observe with one or both eyes when focusing on a central point

What is the structure that carries visual information out of the back of the eye?

optic nerve

Optic Chiasm

X-shaped structure, axons cross to the other side of the brain

Optic Tracts

the retinal ganglion axons after passing through the optic chiasma

Optic Radiations

the axons of the lateral geniculate neurons are grouped as bundles

Where do the axons of the optic radiations typically terminate

pimary visual cortex

Consensual Pupillary Response

response when bright light shines into eyes, both pupils contract

What is indicated if the consensual pupillary response does not occur?

damage to the retina, optic nerve, or brainstem

Stereoscopic Vision

depth perception

Regions of the Ear

outer, middle, and inner

Auricle

a muscular pouch extending from an atrium of the heart that allows the atrium to hold more blood

External Auditory Canal

a tube that carries sound waves from the outside of the head to the eardrum

Tympanic Membrane

eardrum, separates external auditory canal from the middle ear, vibrates

Ceruminous Glands and Cerumen

yellow-brown to gray, earwax

What substance fills the middle ear?

mucous membrane

What structure connects to the middle ear?

pharyngotympanic tube (auditory tube)

What part of the throat does the pharyngotympanic tube connect to?

nasopharynx

What causes ears to "pop"?

pressure being adjusted internally in middle ear to prevent damage to eardrum, tympanic membrane stretching

Auditory Ossicles

malleus, incus, stapes

What structures do the auditory ossicles connect to?

cone-shaped tympanic membrane, connect the tympanic membrane to the oval window

Muscles in the Ear

tensor tympani muscle (tenses tympanic membrane) and stapedius muscle (reduces movement of the ossicles as a unit)

Regions of the Inner Ear

cochlea, vestibule, semicircular canals

Labyrinth

network of winding passages

Endolymph

a fluid with a higher concentration of K+ ions than Na+ ions within the membranous labyrinth

Perilymph

a fluid that has a higher concentration of Na+ ions than K+ ions found between the walls of the bony labyrinth and the membranous labyrinth

Vestibule

the bony portion of the inner ear involved in detecting head position and linear movement

Semicircular Ducts

three tubes of the membranous labyrinth

Semicircular Canals

enclose the ducts

How are the ducts oriented to each other?

right angles to detect rotational movement of the head

Ampulla

an enlarged area at the base of each semicircular duct in the ear that contains receptor cells that detect rotation of the head

What is the name of the opening in the cochlea?

round window- separates the middle and inner ear

What are the three ducts in the cochlea?

cochlear duct (scala media), scala vestibuli, scala tympani

What are the membranes that separate the ducts in the cochlea?

basiler membrane and vestibular membrane