Virginia Tech BMSP 2135 RAT #20

mixed

all spinal nerves are __________ because they are formed from the fusion of an anterior and posterior root

posterior ramus and anterior ramus

a spinal nerve is quite short (1-2 cm)

after it forms and leaves the vertebral cavity, it splits into what two nerves?

posterior ramus

the division/branch of a spinal nerve that travels to the posterior side of the body

anterior ramus

the division/branch of a spinal nerve that travels to the anterior side of the body and/or the upper and lower limbs

true

true or false: Both the anterior and posterior rami are mixed nerves, as they contain sensory and somatic motor axons

rami communicantes (singular: ramus communicans)

another small branch stems from the anterior ramus. These small branches are called _________ ________________________ and they contain visceral motor or autonomic neurons of the sympathetic nervous system.

31

How many pairs of spinal nerves are there?

nerve plexuses

The anterior rami of the cervical, lumbar, and sacral spinal nerves come together and merge to form complicated networks of nerves called what?

spinal nerves

The axons of each spinal nerve cross over one another to enter different plexus branches. For this reason, the muscles supplied by a single branch of a nerve plexus are often served by two or more different ___________ ______________

cervical plexus

a group of nerves consisting of the anterior rami from C1 to C4 that innervates primarily structures around the head and the neck

Located deep in the neck lateral to the 1st-4th cervical vertebrae

Where is the cervical plexus located?

phrenic nerve

The major named motor branch that arises from the cervical plexus is the ______________ __________, which contains axons from C3 to C5, although its main contributor is C4.

diaphragm

The phrenic nerve supplies the _____________ muscle and is the main nerve that drives ventilation

a good mnemonic to remember the roots of the phrenic nerve is "3, 4, 5 to stay alive"

brachial plexus

a group of nerves consisting of the anterior rami from C5 to T1 that innervates structures within and around the upper limb; provides sensory and motor innervation to the upper limb

axillary nerve, radial nerve, musculocutaneous nerve, ulnar nerve, median nerve

What are the five major nerves that arise from the brachial plexus?

thoracic

Except for T1, the nerves coming from the ___________ spinal cord do not form plexuses.

intercostal nerve

Instead, each posterior ramus serves the deep back muscles, and each anterior ramus travels between two ribs as an _______________ __________.

lumbar plexus

a group of nerves consisting of the anterior rami from L1 to L4 that innervates structures within the pelvis and lower limb

psoas major

the lumbar plexus is located anterior to the vertebrae, embedded within the posterior part of the _________________ muscle

femoral nerve

The largest nerve from the posterior division, and of the lumbar plexus as a whole, is the _____________ _______________

sacral plexus

a group of nerves consisting of the anterior rami from L4-S4 that mostly innervates structures of the pelvis and lower limb

sciatic nerve

The largest nerve of the sacral plexus—indeed, the largest and longest nerve in the body—is the __________ ___________

receptors

the basic pathway for sensory information

(1) Stimulus is detected by sensory ______________ of the PNS

(2) Transmitted by PNS sensory neurons to the CNS

(3) Integrated and interpreted by CNS neurons

sensory transduction

the conversion of a sensory stimulus to an electrical signal

nerve endings

sensory transduction occurs at __________ ____________ of somatic sensory neurons; begins at a region of the nerve ending called a sensory receptor, which can be of several types

encapsulated nerve endings, free nerve endings

what are 2 types of sensory receptors?

specialized supportive cells

sensory receptors

encapsulated nerve endings = sensory receptors are surrounded by what?

free nerve endings

sensory receptors

Others are _______ _________ __________ that lack specialized supportive cells and are "naked"

receptor potential

how pressure → AP in a somatic sensory neuron

(1) the stimulus, pressure, opens mechanically gated sodium ion channels

(2) sodium enters the axoplasm, generating a temporary depolarization (_____________ _________________)

spinal cord

how pressure → AP in a somatic sensory neuron

(3) If enough sodium ions enter that the membrane potential reaches threshold, voltage-gated sodium ion channels open

(4) This triggers an AP, which will be propagated along the axon to the _________ _______

adaptation

Different types of sensory receptors respond to stimuli with different speed, intensity, and duration. Some receptors respond rapidly and with high intensity but stop sending the stimuli after a certain period, a phenomenon known as ______________

rapidly adapting receptors

what type of receptor is described below?

- important for detecting the initiation of stimuli, but they ignore ongoing stimuli.

- the reason why you can walk around your home in search of your sunglasses only to find out that they were on top of your head the whole time

slowly adapting receptors

what type of receptor is described below?

- respond to stimuli with constant action potentials that do not diminish with time.

- the reason for the dull, throbbing pain you feel for a week after spraining your ankle

exteroceptors

a sensory receptor that responds to a stimulus exterior to the body

light

exteroceptors

- typically close to the surface of the body

- stimuli such as texture, temperature, and color of an object, chemical odors in the air, and the level of __________

interoceptors

a sensory receptor that responds to a stimulus originating within the body

temperature

interoceptors

- stimuli such as BP, the stretch of an organ such as a skeletal muscle or the urinary bladder, the concentration of certain chemicals in body fluids, and body __________________

mechanoreceptors

sensory receptor that responds to a mechanical deformation of the cell

encapsulated exteroceptors or interoceptors found in the skin, the musculoskeletal system, and many different organs

thermoreceptors

sensory receptor that responds to thermal stimuli; exteroceptors that respond to thermal stimuli, depolarizing in response to temperature changes

chemoreceptors

a sensory receptor that responds to a change in the concentration of a specific chemical in the air or the body's fluids

exteroceptor or interoceptor that depolarizes in response to certain chemicals in body fluids or in the air

photoreceptors

a sensory receptor that responds to a change in light stimuli; special sensory exteroceptors whose membrane potentials change in response to light

nociceptors

a sensory receptor that responds to painful stimuli; generally exteroceptors

proprioceptors

a type of mechanoreceptor that responds to a change in position of a body part, particularly a ligament or tendon

musculoskeletal

proprioceptors are found in the _____________________ system, where they detect the movement and position of a joint or body part

proprioceptors are critical to the integration of sensory and motor functions

mechanically gated ion channels

When a stimuli mechanically deforms the tissue, what type of channel would open?

pseudounipolar

Most sensory neurons are first-order neurons because they are the first neurons to detect and transmit sensory stimuli along the way to the primary somatosensory cortex in the CNS

First-order somatic sensory neurons are ______________________ neurons with 3 main components - a cell body and 2 axons

posterior root ganglion (found lateral to the spinal cord)

Where are the cell bodies of sensory neurons located?

cell body

The peripheral process of the pseudounipolar sensory neuron is a long axon. At one end, it splits into nerve endings; associated with each nerve ending is a sensory receptor. At the other end, the peripheral process terminates near the neuron's _______ ________.

posterior horn

The central process of the pseudounipolar sensory neuron exits the cell body and travels through the posterior root of the spinal cord to enter the ___________ _________ of the spinal cord (or into the brainstem for cranial nerves).

central process

Note that an AP which begins at the sensory receptors located on nerve endings will be propagated to the end of the ____________ ____________.

axon diameter, thickness of myelin sheath

What two factors determine the speed of transmission of axons?

proprioceptive

The axons with the largest diameter and the thickest myelin sheaths conduct impulses the fastest.

Such axons include those that convey __________________ stimuli to the CNS.

It's critical for these stimuli to travel quickly because the CNS needs them to make adjustments during movement to maintain posture and balance

pain, temperature

The smallest-diameter axons with the least amount of myelin transmit action potentials the slowest.

Both _______ and __________________ stimuli are conveyed to the CNS by such axons.

Indeed, conduction through these axons is so slow that a noticeable delay occurs between the initiation of the stimulus and its interpretation by the CNS.

throbbing

pain and temperature stimuli being conveyed to the CNS by small diameter axons with the least amount of myelin is responsible for

(1) after you touch an object, it may take a moment to determine whether it is hot or cold.

(2) the "________________" nature of pain—each "wave" of pain you feel is actually one continuous stimulus.

fingertips

The skin of the (forearm/fingertips) is richly innervated with sensory neurons, and each of these neurons has a relatively small receptive field

larger

the skin of the forearm is innervated by a much smaller number of neurons, so each neuron has a somewhat (smaller/larger) receptive field

forearm sensory neurons

Which has a larger sensory field, sensory neurons on the fingertip or on the forearm?

small

The relative sizes of receptive fields can be measured by the two-point discrimination threshold.

In this test, two stimuli (usually a pair of calipers or applicator sticks) are placed closely together on the skin. The stimuli are then moved apart until the subject can feel two distinct points. The two-point discrimination threshold for the fingertips is quite (small, large) (about 3 mm) compared to that of the forearm (about 40 mm).

dermatome

A _________________ is a segment of the skin. Each is determined by the spinal nerve that serves it with somatic sensation.

referred pain

painful stimuli that are perceived as cutaneous pain along a specific dermatome

dermatome

referred pain

- pain that originates in an organ is perceived as cutaneous pain

- the pain is generally located along the _______________ for that nerve

- example: pain caused by a heart attack is often perceived as pain in the anterior chest wall and left arm

- this is because the first-order visceral sensory neurons from the heart travel with the first-order somatic sensory neurons of the T1-T5 dermatomes, which map to the anterior chest wall and arm

refraction

bending of light rays when they pass through a translucent object

cornea

The greatest degree of refraction—about two-thirds of the eye's refractive power—occurs as light passes from air through the ____________, which has a refractive index similar to that of water.

emmetropic (or emmetropia)

When the eye is relaxed and focusing on a distant object, this is known as the ______________ state of the eye

accommodation

the rounding of the lens to focus light from near objects on the retina

contracts, closer to, decreases

accommodation

- ciliary muscle (contracts/relaxes)

- ciliary body moves (closer to/away from) the lens

- this (increases, decreases) tension on the suspensory ligament

photoreceptors

the retina consists of two layers, an outer pigmented epithelium and an inner layer that contains ____________________ and other cell types arranged in layers

rods, cones

What are the two types of photoreceptor?

pigmented

the photoreceptors (rods and cons) are located adjacent/deep to the ___________________ layer of the retina

bipolar cells

The photoreceptors synapse with neurons called __________ _________, which communicate with retinal ganglion cells, the most anterior cells in the retina

optic nerve (CN II)

The axons of the retinal ganglion cells course across the retinal surface and form the what?

retinal ganglion cells, bipolar cells

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

color

Cones = photoreceptors that have a cone-shaped outer segment and respond to wavelengths of light that we perceive as ________; responsible for high-acuity color vision

in bright light (cannot respond at all in the dark)

cones function best in what type of light?

rods

Cones are nonfunctional at night, so only the ______ can produce the images you see, resulting in low-acuity, grayscale images

fovea centralis

cones are highly concentrated in the _________ ____________ → allows us to focus on an object

No cones found at the very edge of the retina

dim

Rods = photoreceptors that have a rod-shaped outer segment and that are sensitive to low-light conditions; responsible for low-acuity, black and white vision in ______ light

night vision

rods

- cannot detect color

- cannot function in bright light

- extremely sensitive to dim light

- reason for ________ _______

no

rods are more concentrated away from the fovea centralis

are there any rods in the fovea centralis?

Concentration of rods in the outer retina makes them important for peripheral vision, or detecting images at the edge of our vision

synaptic terminals

basic parts of a rod and cone

(1) ___________ _______________, which are the most anterior portion that contact bipolar cells

(2) cell bodies with nuclei

(3) inner segments that contain mitochondria and the typical cellular organelles

(4) outer segments that are on the side closer to the pigmented layer.

flattened discs

The outer segments of the photoreceptors house stacks of ____________ ________ that absorb light and are formed from segments of the plasma membrane. They have a lifespan of only 10-12 days, and then they are shed by the photoreceptor and phagocytosed by the cells of the pigmented layer.

rhodopsin

Each disc membrane of a rod contains the pigment _____________

opsin (protein), retinal (pigment)

What are the two components of rhodopsin (the pigment found in each disc membrane of a rod)?

wavelengths

cones are named because of the shape of their outer segment, which contains discs composed of infoldings of the plasma membrane.

The discs contain the pigment iodopsin, which is made of two components: retinal and the protein photopsin.

Photopsin is similar to opsin but has a slightly altered structure that allows it to absorb different _______________ of light.

blue, green, or red

Three forms of photopsin respond to wavelengths we perceive as what 3 cone pigments?

The color pigments react to slightly overlapping ranges of wavelengths, so that our perception of each color is generated by stimulation of varying combinations of cone populations

For example, red light stimulates primarily red cones, but orange light stimulates red cones and some green cones as well

cone pigments

When a person has a defective gene for one or more ______ _____________, color blindness results.

grayish-brown

The most common form of color blindness causes the red or green cone to absorb the wrong wavelength of light, resulting in red-green color blindness.

Affected people have difficulty in distinguishing red from green; both colors appear _______________

sex-linked disorder

color blindness is more common in males, which indicates that color blindness is a what?

retina

There is a fundamental difference between transduction in the ________ and that in other special senses.

depolarizing

differences in signal transduction between visual system and other special senses

1) Recall that olfactory neurons and gustatory cells detect smell and taste stimuli and respond by ___________________ and signaling another cell; in other words, the olfactory neurons and gustatory cells are "off" until they are turned "on" by a stimulus.

hyperpolarizes

differences in signal transduction between visual system and other special senses

2) In the visual system, the process is reversed.

- In the dark (the absence of a stimulus), the photoreceptor cells are depolarized ("on") and continually release neurotransmitters onto adjacent neurons.

- The presence of light ________________ the photoreceptor (turns it "off") and reduces the release of neurotransmitters, which alters the activity of other cells in the retina and sends that information to the brain.

- The end result is the same: The nervous system detects a change in the environment and transduces it into an action potential.

more

there are (more/less) photoreceptors than retinal ganglion cells in the retina

photoreceptor

despite there being more photoreceptors than retinal ganglion cells, vision is sharpest when a ganglion cell receives input from only a single ____________________.

This is the case in the fovea, where one cone may synapse with only two bipolar cells, which in turn contact only one retinal ganglion cell.

For this reason, sharp vision is possible here, because when a specific ganglion cell is stimulated, the brain knows exactly which tiny part of the retina (and the visual field) has been stimulated.

edges

peripheral vision

Toward the __________ of the retina, however, hundreds or thousands of photoreceptors contact a small number of bipolar cells, which then synapse with one retinal ganglion cell.

The retinal ganglion cell cannot determine exactly which one of the photoreceptors has been stimulated, so the brain does not receive precise visual information.

less

So, peripheral vision is (more/less) detailed than central vision, which explains why you can clearly read the menu at a restaurant but not immediately recognize a friend who walks up beside you.

visual field

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

optic nerve

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

optic chiasm

an X-shaped structure formed by the meeting of the optic nerves at the midline; location where some of the axons of the optic nerve cross to the other side of the brain

optic tracts

After passing through the optic chiasma, the retinal ganglion axons are called the ________ _________

thalamus

Most of the axons of the optic tracts end in the _____________; visual stimuli travel from the thalamus to the primary visual cortex in the medial portion of the occipital lobe.