Neuro Exam 2

All sensory systems share the following features:

sensory receptor cells, transduction, neural pathways, primary cortical area, higher cortical area

Sensory receptor cells

responds to external changes in energy (chemical, mechanical, thermal)

Transduction

converts chemical, mechanical, or thermal energy into activity for neurons

Neural pathways

carries sensory information to other brain regions

Primary cortical area

receives sensory information

Higher cortical areas

give rise to sensory perception/identification

Mechanoreceptors

sensitive to touch and pressure

Merkel’s disks (M)

respond to light touch

Meissner’s corpuscles (M)

respond to touch and slow vibrations

Ruffini endings (M)

respond to stretching of the skin (pressure) and warmth

Pacinian corpuscles (M)

respond to brief, deep pressure and rapid vibrations

Nociceptors

sensitive to painful stimuli

Thermal (N)

respond to intense heat

Chemical (N)

detect chemical toxins

Mechanical (N)

respond to intense pressure (pinch, scratch, cut)

Transmission along a neural pathway (1)

sensory receptor (somatosensory neuron) sends signal along axons terminals to spinal cord

Transmission along a neural pathway (2)

from spinal cord, signal is sent to thalamus (ventral posterior nucleus)

Transmission along a neural pathway (3)

a thalamic neuron send the signal to the somatosensory cortex of the parietal lobes

Transduction (somatosenation)

touch, pressure or irritants (physical stimulus) activate sensory receptors in skin including mechanoreceptors and nociceptors

Transmission along a neural pathway (somatosenation)

mechanoreceptors and nociceptors sends signal along axon terminals to spinal cord, from spinal cord signal is sent to thalamus then to the somatosensory cortex of the parietal lobes

Primary somatosensory cortex (somatosenation)

areas of the body that are represented by the largest areas of the primary somatosensory cortex are those with greatest sensitivity to touch

Large areas of the primary somatosensory cortex

dedicated to the face

Much larger area of the primary somatosensory cortex

dedicated to the fingers compared to the toes

So what determines the two-point discrimination ability?

receptor density and size of their receptive fields

For a probe/touch to stimulate one or more…

sensory receptors must be packed closely enough

To be able to connect with different CNS neurons, dense neighboring receptors…

must have small receptive fields

Receptive field

specific region of sensory space (skin, visual stimulus) that can drive an electrical response in a sensory neuron

on the back of each sensory receptor…

gathers information from a much larger skin area than a receptor on the fingertip

for a person to feel two points…

two separate neuronal populations must be activated by stimulation of their respective receptive fields

Taste (gustation) & smell (olfaction) are called … because …

chemical senses; both have sensory receptors that respond to molecules in the food we eat & air we breathe

Olfactory nerve

sense of smell

Why can you taste & smell food at the same time?

nose and mouth are connected through the same airway

Can you taste without being able to smell?

without smell, we are limited to recognizing 5 distinct sensations: salty, sweet, bitter, sour & savory (umami); all others come from smell

There are > 400 … receptors vs 5 … receptors

olfactory, gustatory

Our sense of smell is responsible for … of what we taste

80%

When you take a bite of cake, what must occur for its tastant chemicals to reach the taste receptors?

chemicals in food dissolve in saliva, move through a central pore in the taste bud and bind to taste receptors

What are the neurons that carry the taste information to the brainstem>

activation of a taste receptor activates cranial nerves (Facial, Glossopharyngeal, Trigeminal, Vagus), which carries the taste information to brainstem (medulla)

From tongue to gustatory index

chemicals in food dissolves in saliva to bind to taste receptors, taste buds contains taste receptor cells, they synapse upon cranial nerves that carries taste signals to solitary nucleus of medulla, signal is then sent to thalamus and finally to gustatory index

Trigeminal nerve

sensations in your face & cheeks, taste and jaw movements

Facial nerve

facial expressions and sense of taste

Glossopharyngeal nerve

ability to taste and swallow

Vagus nerve

digestion and heart rate

Hair cells in the inner ear play the most important role in the auditory system. What are they?

hair cells are the sensory receptors of the auditory system

How do hair cells function?

in response to soundwaves, they sit above the basilar membrane & move up and down and bump against the tectorial membrane

When bumping against the tectorial membrane, hair cells …

bend, depolarize, and transmit signals to the auditory nerve

3 steps that allow sound waves to cause fluid to vibrate inside the cochlea (1)

sound waves (physical stimulus) causes vibrations of the eardrum (outer ear)

3 steps that allow sound waves to cause fluid to vibrate inside the cochlea (2)

vibrations of the eardrum causes ossicles (3 small bones: malleus, incus, stapes) within the middle ear to vibrate

3 steps that allow sound waves to cause fluid to vibrate inside the cochlea (3)

ossicles cause vibration to fluid in the cochlea (spiral-shaped structure in inner ear)

oscillations of fluid in the cochlea causes the hair cells to …, causes …

bend and become activated; neural signals to travel along the auditory nerve to the brain

Is the auditory nerve part of the CNS (Central Nervous System) or PNS (Peripheral Nervous System)?

PNS (Peripheral Nervous System)?

Does the auditory nerve require the spinal cord?

No

What is the specific cranial nerve name?

auditory/vestibular (vestibulocochlear) nerve

Auditory/vestibular (vestibulocochlear) nerve

sense of hearing and balance

optic nerve

ability to see

Does release of neurotransmitter into the neuromuscular junction inhibit muscle fiber contraction?

No

1st Way to inhibit movement

alpha motor neuron stops firing so ACh is no longer released

2nd Way to inhibit movement

contraction of antagonistic muscle pairs (e.g freezing, try moving then freeze)

Primary Motor Cortex (precentral gyrus)

communicates directly with the spinal cord and contains a somatotopic organization

Premotor Cortex

prepares and integrates behavioral actions (e.g reaching and grasping objects) like an “action map”

Supplementary motor area is active …

during conscious desires to move when stimulated

Mirror neurons

provides bridge between observation and action and a mechanism for imitation; active when observe and perform action

Prefrontal Cortex

keeps goals in mind & is important for deciding which actions to perform, inhibiting inappropriate actions and directing purposeful movements

Primary motor cortex sits in … front of the central sulcus while the somatosensory cortex sits … it

front, behind

Primary somatosensory cortex (…) send tactile feedback to the primary motor cortex (…)

(parietal lobe), (frontal lobe)

If you disrupt … input to fingers then lose ability to do … tasks

sensory, fine motor

Precentral gyrus

contains the primary motor cortex

Postcentral gyrus

contains the primary somatosensory cortex

Does the brain choose our actions before we become aware of our choice?

yes, activity arising in the supplementary motor area reliably precedes the decision to act

EEG readiness potential preceded urge to move by …

1 second

Mirror neurons are active when …

observe and when we perform an action (reach, smile, walk)

Striatum

the input region of the basal ganglia

Caudate

receives strong input from PFC and necessary for goal-oriented behavior

Putamen

receives strong input from motor and premotor cortex and necessary for automatized behavior

Globus pallidus

control outputs of basal ganglia

Direct pathway

implicated in maintenance of thoughts, emotions and actions, habits

Indirect pathway

implicated in interruption/redirection of thoughts, emotions and actions

Cerebellum

predicts consequences of movement before it occurs based on learning and feedback about accuracy and timing

Cerebellum is involved in … and …

movement accuracy, balance

PFC (prefrontal cortex) generates a goal to take a … and involved in …

movement, inhibition of inappropriate action

… and … motor cortex translate this goal from the PFC into … via signals to the …

premotor, primary, action, spinal cord

Cerebellum and basal ganglia

modify movement commands to increase accuracy and automaticity of/habitual movements, respectively

… regions of … cortex adjusts … based on … feedback

Sensorimotor, parietal, movement, sensory

Spinal cord communicates … with … to move body

directly, muscles

A brain area with … organization contains … that represent …

somatotopic, different regions, different body parts

In the largest parts of the brain, …, …, …, gets distorted and represented

lips, face, fingers

Central pattern generators (CPGs)

a set of neurons that control repetitive behaviors like walking, chewing, breathing; located in the spinal cord and brain stem that can be performed without awareness

Flexion and extension movements are … in direction

opposite

As muscle fibers connecting 2 bones contract, the bones may move … together causing a … (e.g of flexor: bicep muscle)

closer, flexion

As these muscles fibers relax and other muscle fibers contract the bones move … for an … (e.g of extensor: tricep muscle)

farther apart, extension

Alpha motor neurons release … at the axon terminal which crosses the … (neuromuscular junction) to reach the …

acetylcholine (ACh), synapse, muscle fiber

Muscle fiber contains … (an ACh receptor)

nicotinic receptors

When Ach binds to the receptor, the … open in the muscle fiber initiating process that leads to …

Na+ channels, muscle contraction

Each muscles is comprised of … of … of threadlike cells called …

100s, 1000s, muscle fibers

A single alpha neuron can target 1000s of muscle fibers (e.g back of leg), what type of connection is this? recurrent, divergent, or convergent?

divergent

The alpha motor neurons’ axons exit the … and … on …

spinal cord, synapse, muscle fibers

Alpha motor neurons originate in the … in the … and carry info to muscles that move … and … from … down

spinal cord, gray matter, limbs, other body parts, neck

… enter the dorsal horn

Sensory neurons’ axons

… carries info between … and …

surrounding white matter, brain, spinal cord

… exit from the ventral horn to reach the …

alpha motor neurons’ axons, muscles

Spinal cord is comprised of major regions that control movements in different body parts:

cervical, thoracic, lumbar, sacral