PBSI 235 EXAM 2

Differentiate between skeletal muscles, muscle synergists, and muscle antagonists

• Skeletal muscles: produce bodily motion by contracting and pulling on the skeleton, tendons connect the muscle to the bones

  • they are also made of striate muscle, layers of actin and myosin which make up myofilaments that control the muscle contraction, giving it a striped appearance

• Muscle synergists: work TOGETHER is order to execute motion (brachialis)

• Muscle antagonists: work in OPPOSITION to one another, when one contracts, the other stretches (tricep brachii)

What are the two types of muscle fiber? What sets the apart from one another?

Fast twitch fibers: contract quickly and fatigue easily

Slow twitch fibers: contract slowly with less intensity, but fatigue mor slowly

Name three characteristics of motor neurons

• have cell bodies in the central nervous system (spinal cord and hindbrain)

• axons that form the efferent portion of the peripheral nerves

• axon terminals that synapse on muscle fibers

How is acetylcholine released onto the postsynaptic membrane in motor neurons?

through neuromuscular junction,

• which is the synapse that motor neurons form on muscle fibers. The terminals of these motor neurons release the acetylcholine onto the post-synaptic membrane.

How many motor neurons does it take to contact multiple muscle fibers?

ONE

aka one motor unit, a single motor neuron and all of the muscle fibers it contacts

• one motor neuron contacts multiple muscle fibers generally

What pathway involves cell bodies in the primary motor cortex with axons that form synapses on motor neurons in the spinal cord?

pyramidal motor system

what controls muscles in distinct parts of the body?

Primary motor cortex:

aka M1, on the precentral gyrus of the frontal lobe, and it contains a motor map of the body arranged topographically, and muscles in distinct parts of the body are controlled by distinct regions in M1

where do cell bodies in the primary motor cortex (M1) synapse?

on motor neurons on the contralateral (opposite) side of the body because axons arising in the motor cortex head off in an inferior (down) direction, crossing the midline at the medulla.

What direction is activity in primary motor cortex neruons associated with?

inferior (down), crossing the midline at the medulla

Describe the non-primary motor cortex

• broadly involved in motor planning, where these regions prepare specific sequences of voluntary motion executed by the primary motor cortex

• includes the supplementary motor areas, thought to generate motor programs for preplanned movement, and the premotor cortex, thought to generate motor programs in reaction to external events

What does the extrapyramidal motor system regulate? Describe one of its central components

the pyramidal motor system via specific thalamic nuclei that project to primary and nonprimary motor cortex which include the basal ganglia and cerebellum

• basal ganglia: area of forebrain that recieves heavy dopamine from midbrain, also contains ‘stop’ and go’ pathways that when activated, can initiate or halt behavior respectively

• cerebellum: hindbrain region that has more neurons than the cortex and is semi-mysterious in function but is known to contribute to precision motor control

How do the basal ganglia and cerebellum influence motor cortices?

via largely parallel pathways through the nuclei of the ventral anterior and ventral lateral nuclei (VA/VL complex) of the thalamus

what is the effect of dopamine release?

dopamine generally excites neurons that express D1-like receptor and generally inhibit neurons that express D2-like receptors, usually the effect of dopamine release is to increase movement.

nigrostriatal pathway

cell bodies in the substantia nigra (midbrain) send axons to the dorsal striatum (basal ganglia)

what environmental stimuli do specialized sensory systems detect?

this allows your brains to build a representation of the world around you

• specific forms of energy (light, sound waves, etc.)

• particular chemicals (odors, tastes)

explain sensory transduction

animals have sensory organs that have receptor cells are specific for detection of energies and chemicals in their environment, these receptor cells convert this sensory input into an electrical signal to be processes and interpreted by the nervous system, this conversion is known as sensory transduction

• once transduction has occured, the stimulus is encoded as a stream of action potentials travelling toward the brain via peripheral nerves

if two species both possess a given sense, will they percieve the same stimuli

no, sensory receptors can be tuned differently even if they are designed to detect the same energy

how many types of receptor cells can one sensory system have?

there can be multiple, allowing you to distinguish inouts that are both qualitatively and quantitatively different

what are receptive fields

the area which a receptor cell can detect a stimulus

differentiate between phasic and tonic receptors

sensory adaptation: progressive decrease in a receptor’s response to a sustained stimulus

• phasic receptors: display adaptation, less engaged when the stimulus is constant; the decrease in the signal coming from the phasic receptor allows the brain to ignore an unchanging, harmless stimulus

• tonic receptors: respond as long as the stimulus is present, reminds the brain even if it isn’t worth much attention

where do the earliest stages of perception occur

primary sensory cortex (brain), recieves senosry infor from the thalamus

what cortex processes touch information? sound information?

• somatosensory cortex: processes touch and has a map of the skin surface (somatotopic map)

• auditory cortex: processes sound information (tonotopic map)

where do association cortices recieve information from

aka nonprimary cortices, receive information from the primary sensory cortex and integrate inputs from multiple senses

• may cause synesthesia, a stimulus in one sense modality also causes a sensation in another

describe plasticity

a change as a result of experience; extensive or highly skilled use of a body part that can expand its representation in the somatosensory cortex (playing the violin)

where is the primary somatosensory cortex located

The postcentral gyrus of the parietal lobe/ behind the central sulcus. 

what is proprioception

perception of the position of limbs and body in space

• involves specialized reeptors that detect stretch in tendons, contraction of muscles, and joint angle

are pacinian corpusles tonic or phasic receptors

receptor specializes for sensing pressure and texture. they are phasic receptors, adapt quickly to a constant stimulus

what determines whether or not an action potential is fired in dorsal root ganglia neurons

the summation of generator potentials

explain the pathway from DRG to the primary somatosensory cortex

• axons of DRG neurons travel up spinal cord up to medulla

• DRG neurons form synapses on medulla neurons

• medulla neurons sends axons across midline, forming synapses on neurons in the contralateral ventral posterior nucleus (VPN) of the thalamus

• stimuli on the left side of the body are processed on the rights side of the brain and vice versa

what does the amplitude of the wave determine

• volume. loudness, or intensity of a sound

what does the frequency of the wave determine

the pitch of a sound: lower pitch has fewer waves, while high pitch has more waves (Hz)

what comprises the external ear

• pinna: fleshy exterior

• ear canal/auditory canal: passage connecting pinna to ear drum

Describe each of the components of the middle ear. 

Tympanic membrane: translates sound into vibrations 

Ossicles: vibrations pass through, connecting to the oval window

Oval window: membrane through which sound enters the ear

Explain the role of the cochlea and its Organ of Corti

Cochlea: semicircular canals which contain fluid. Vibrations from the ossicles enter the cochlea and it turns into pressure waves

Organ of Corti: specialized part of cochlea that understands pressure waves

• Also contains the basilar membrane

How do certain areas of the basilar membrane differ?

Each region of the basilar membrane responds to a specific sound frequency, arranged along its length from highest to lowest. The area of the basilar membrane nearest the base (closest to the oval window) of the cochlea responds to the highest frequencies, and the area nearest to the apex (farthest from the oval window) responds to the lowest

What are hair cells and what do they have that don’t flex in response to sound?

They are receptors that transduce sound into electrical activity and  they have stereocilia

How is a generator potential created and what does it cause?

Deflection or displacement of the stereocilia opens mechanically-gated ion channels which causes the generator potential 

This cause voltage-gated calcium channels to open, causing the release of glutamate

What are the EPSPs created by glutamate (released from hair cells) able to do?

They can immediately generate an action potential that is conducted through the cell body (spiral ganglion) down the vestibulcochlear nerve and onto the CNS

Explain auditory pathways

Spiral ganglion neurons synapse on the neurons of the cochlear nucleus in the medulla. Axons from the cochlear nucleus cross the midline and synapse on the neurons of the superior olivary nucleus in the pons

How is sound localized?

By comparing the difference in how it strikes both ears. Also through timing and volume, as well as the superior olivary nucleus receiving input from both ipsi- and contralaterally

What does the organization of the primary auditory cortex (A1) reflect?

A1 reflects the way that the basilar membrane responds to increasing frequencies along its length

What happens if spiral ganglion cells are deprived of input? What does this lead to or cause?

Spiral ganglion cells may die if deprived of input. This can cause tinnitus, a ringing in the ears

List the three directions in which the head can rotate

Pitch ( up and down), Yaw (back and forth), Roll ( moving side to sides)

What do the receptors within the ampulla detect? Additionally, which structure does this contain (and what happens when it deflects)?

Head rotation, contains cupula, which when deflected will displace stereocilia and open mechanically-gated ion channels

Which parts of the semicircular canals detect linear motion

Utricle and Saccule

What happens when the vestibular ganglion is depolarized

Vestibular hair cells release glutamate onto vestibular ganglion neurons, which are very similar to spiral ganglion neurons

Describe the vestibular-ocular reflex.

Sensation of movement in one direction causes the eye to move in the opposite direction to stabilize visual images

What are the three elements of inputs that contribute to flavor

Taste (gustatory) , smell (olfactory), and somatosensory

Where are the taste buds located? What is their role in taste?

Located in different areas on the tongue, embedded in papillae

What are some characteristics of filiform papillae

Do not contain taste buds, and only have somatosensory receptors

What are the five basic tastes our tongues can distinguish

Salty, Bitter, Sour, Umami (savory), and Sweet

Is the ATP release caused by taste receptor cells spatially targeted?

NO, ATP release is on specific nerve endings and does not involve well defined presynaptic membrane

Does the entrance of sodium into receptor cells hyperpolarize or depolarize the cell? How is ATP released

Depolarize

What kind of ion channels to taste receptors that respond to sour have? How is ATP released?

Hydrogen ion channels, and ATP is released through the depolarization of the cell, causing the calcium channels to trigger its release

Describe the action of T1R receptors for sweet taste. After they bind to sugars, what ensues

They bind to sugars and other sweet-tasting chemicals, When they bind to sugars, the receptors then bind to each other, forming a dimer (a compound molecule made of two similar or identical

subunits)

What happens once dimerized T1R receptors activate G-proteins inside the taste receptor cell?

Dimerized T1R receptors activate G-proteins inside the taste receptor cell, which can depolarize it and cause ATP release

How do amino acids, such as glutamate, cause umami taste

Glutamate binds to metabotropic glutamate receptors on taste receptor cells, activating G-proteins on the inside of the cells, depolarizing them, and leading to ATP release

How do chemicals cause bitter taste? Make sure to discuss T2R receptors in your answer

They all bind to T2R receptors, of which there are 2-3 dozen types. These also activate G-proteins, which depolarizes receptor cells and causes ATP release

Describe the gustatory pathway. What makes this pathway unique from other sensory pathways

Taste receptor cells release ATP onto the nerve endings of neurons with cell bodies in the ganglia of 3 cranial nerves. These neurons project to the nucleus of the solitary tract in the medulla, which projects to the ventral posterior nucleus of the thalamus, which projects to the

gustatory cortex in the insula and parietal lobe. Unlike other sensory pathways, the gustatory pathway is ipsilateral – meaning taste input from the left side of the tongue is processed on the left side of the brain

How does smell play an important role in flavor?

Plays an important role in flavor because there are far more distinct odors than there are distinct tastes

Where are olfactory receptor cells located?

Olfactory epithelium

Describe the relationship between G-proteins activation inside the olfactory receptor cell and the firing of action potentials

Olfactory receptor proteins activate G-proteins inside the olfactory receptor cell, producing a generator potential that can cause the cell to fire action potentials

List glomeruli characteristics and talk about where they receive input from.

• areas of synaptic connectivity

• contain the axons of olfactory receptor cells and the dendrites of mitral cells

• Carry olfactory information elsewhere in the brain 

• Receives input from olfactory receptors that express one specific olfactory receptor protein

Does olfactory information pass through the thalamus on the way to the cortex

No, it goes to the cortex without passing through the thalamus

Which organ detects pheromones? Name two actions pheromones play a role in

Vomeronasal Organ, pheromones play a role in courtship and signaling genetic relationships, as well as predator evasion

How can dogs detect the presence of drugs more efficiently than man-made devices

have an incredibly sensitive olfactory apparatus, and can detect odors at concentrations as low as 2 parts per trillion

What determines the brightness of light?

Amplitude of waves

What is the trend of wavelength from purple light to red light?

Wavelength increases from purple to red light

What are the three primary parts of the eye we covered

Retina: thin layer of tissue at the back of the eye that transduces light to a neural signal 

Cornea: fixed transparent piece of tissue refracts light 

Lens: flexible and changes shape to further refract light

What category of retinal cells do rods and cones fall into? Make a table to compare the two of these cells

photoreceptors

RODS:

• Sensitive to low levels of light 

• Designed for lower acuity vision 

• Insensitive to color 

• Higher number in periphery

CONES:

• Require higher levels of light 

• Designed for higher acuity vision 

• Different cones respond to different wavelengths of light 

• Higher number in center of retina (fovea) 

What happens when opsins are struck by light

They activate G-proteins that indirectly close ion channels and cause the neuron to depolarize

If photoreceptors are depolarized, what happens in comparison to when they are hyperpolarized

When photoreceptors are hyperpolarized they release less glutamate

How do on-center and off-center bipolar cells function? How do bipolar cells compare to photoreceptors?

On-center: inhibited by glutamate 

Off-center: excited by glutamate

Bipolar cells do not have action potentials, but also release glutamates when depolarized 

Describe the activity of retinal ganglion cells

• Receive glutamate from bipolar cells 

• On-center ganglion cells receive input from on-center bipolar cells off-center receive input from off-center bipolar

What are the two factors that explain why visual acuity is highest at the fovea

• More cones in the fovea 

• Retina is thinner at fovea, less tissue for light to pass through

What structure do many animals have that allow them to make good use of night vision

Tapetum lucidum

What characteristic of the optic disc makes it the blind spot of the retina

This is where the axons of ganglion cells and blood vessels exit the eye 

There are also no photo receptors in this area and it is insensitive to light

Describe light level adaptation. How does the pupil play a role in this?

Change in sensitivity to the brightness of intensity of light. 

The pupil is the open space in the iris that allows light into the eye. It can expand or contract to allow in more or less light

Describe the relationship of stimulation and detection between light levels between cones and rods

Rods & cones are sensitive to different levels of light. Individual rods may be able to detect light at the lowest possible level, the minimal light necessary to stimulate cones is roughly the maximum amount that rods can detect

How is photoreceptor adaptation related to range fractionation?

Within the broad range of light levels that rods & cones respond to (range refraction), these cells can adjust their level of sensitivity, (photoreceptor adaptation). If there is a big, sudden change in light levels, a photoreceptor will adjust its level of light sensitivity to match, becoming more or less sensitive, as appropriate

How many cones does the typical human retina have? How does this compare to other species?

Typically 3, other species may have 1 or 2 or even 16 extra

How does color blindness show the importance of opsins

Genes for opsins in the M and L cones are on the X chromosome, when we see a defect in this gene it results in red-green color blindness

What area makes up the visual field?

The area that is visible to you without having to adjust your gaze

How do retinas receive input in humans? Are both retinas involved

Both retinas receive input from the left and right side of the visual field

Differentiate between the two retina halves

Nasal retina: half closest to the nose 

Temporal retina: half closest to temple  

Left half of each receive  input from right, and right half receive input from the left

Describe how light from the left visual field would then be transmitted in the retina

Left half of each receive  input from right, and right half receive input from the left

How does the position of the eyes in the head differ between prey animals and predators?

The position of the eyes in the head determines the degree to which light from the left and right visual fields strikes both eyes. Prey will have eyes further apart for wider visual field, predator will have eyes in front of their head to create depth perception

What forms the optic nerve

Axons from the ganglion cells

What happens when axons cross at the optic chiasm? What does this process allow

Visual information from the left nasal retina and right temporal retina are now on the right side of the brain. This allows the left visual field to be processed by the right side of the brain (and vice versa)

What happens before retinal ganglion cells form synapses on neurons in the LGN?

Retinal ganglion cells axons travel from the optic nerve to the optic tract

What area is important for circadian rhythm? What input allows the brain to sync the rhythm with light levels?

Suprachiasmatic nucleus of hypothalamus. Retinal input allows the brain to sync the rhythm

Describe the two principles of cortical processing of visual information

• Hierarchical model of visual processing: moving inward from the eye, each level of the visual system works by combining inputs from the level before it to create  increasingly complex representations

• Fragmented visual processing: distinct regions are specialized for specific aspects of vision. No one area processes the totality of visual perception

What is meant by the primary visual cortex (V1) being a map of the visible world covered by the two eyes?

A given part of the visual field will always be processed by the same part of V,  nearby parts of the visual field are processed by nearby parts of V1

Compare simple and complex cells

Simple cells respond to bars of a certain orientation in the narrow, linear region of the visual field preferred by a given cell. Each will respond to either a light or a dark bar, but not both (complex-not important): Complex cells are thought to receive inputs from multiple simple cells and thus sum their activity

What can cause agnosia

Can be caused by destruction of V1 and/or its inputs

• Acquired deficit in perception often stemming from brain damage

What kind of connections does the primary visual cortex have with the non-primary visual cortex?

There are reciprocal connections between V1 (primary)  and V2 (non-primary

Describe the split off from V2 that occurs for dorsal and ventral streams

Dorsal: V2 V5 posterior parietal lobe (‘where’, visuospatial processing related to the control of motion)

Ventral: V2 V4 inferior temporal lobe (‘what’, recognition of visual stimuli)

What is the MT primarily concerned with? If damage is incurred, what happens? , damage can occur to MT and cause , where someone is unable to process visual motion

visual motion

causes akinetopsia, or motion blindness

visual images appear as a series of stills where objects leap from one position to another instead of a smooth transition like a strobe light

Elaborate on the role of the posterior parietal lobe

Contains a number of sub-regions with neurons that respond to the sensory properties of objects or to motor acts in which the subject (usually a monkey) interacts with an object. Highly connected to motor cortices, thought to be crucial for integrating vision into the control of motion

What is the V4 thought to integrate?

Information from earlier stages of visual processing to represent the basic features of objects that allow them to stand out from the background