NEURO Exam 2

What are Skeletal Muscles?

used to produce bodily motion by contracting (muscles do not push) and pulling on the skeleton. Tendons connect the muscles to the bones

What are muscle synergists?

work together in order to execute motion (ex: pectorals and deltoids (shoulders) work together a lot)

What are muscle antagonists?

work in opposition to one another. When one contracts, the other stretches (ex: bicep and tricep are muscle antagonists)

What are skeletal muscles made of?

made of striate muscle-overlapping layers of myosin and actin, which make up the myofilaments that control muscle contraction (give the striped appearance), give these muscles a striped appearance (compared to smooth muscle that is autonomic system)

What are muscle fibers?

the result of multiple cells fusing during development, and have multiple nuclei (long multi celled structures; become one long fiber)

1. (once fusion occurs that’s what you’re going to have for life; getting bigger at the gym is adding myofilaments not muscle fibers) 

What are the types of muscle fibers?

Fast twitch fibers and slow-twitch fibers

What are fast twitch fibers?

contract quickly and fatigue easily (any effort)

What are slow-twitch fibers?

contract slowly and with less intensity, but fatigue more slowly (sustained effort; continued period of contracting a muscle)

What are motor neurons?

have cell bodies in the central nervous system (spinal cord), axons that form the efferent portion of the peripheral nerves, and axon terminals that synapse on muscle fibers

What is the neuromuscular junction?

the synapse that motor neurons form on muscle fibers. (where the nervous system talks to muscles) The terminals of motor neurons release acetylcholine onto the muscle fiber postsynaptic membrane; triggers contraction  

What is a motor unit?

a motor neuron and all of the muscle fibers it contacts. In general, one motor neuron contacts multiple muscle fibers (one to many relationship)

What is the pyramidal motor system?

pathway involving cell bodies in primary motor cortex with axons that form synapses on motor neurons in spinal cord (passes through white matter all the way to spinal cord)

What is the primary motor cortex?

also called M1, located on the precentral gyrus(hills) of the frontal lobe. Contains a motor map of the body arranged topographically (muscles in distinct parts of the body are controlled by distinct regions in M1) body parts are represented in one place on M1; not in proportion in size in M1, meaning hands have a big part; size is more about fine motor skills; precise motion requires more muscles so needs more cortex to make this happen) hands and face are big

Axons arising in primary motor cortex head off in an inferior direction, crossing the midline at the medulla; what does this mean?

cell bodies in the primary motor cortex synapse on motor neurons on the contralateral side of the body (means that left side of brain control right side of body; right side of brain controls left side of body)

Activity in primary motor cortex neurons is often associated with what?

the direction of a movement (correlated with motion). Thus, when a limb moves in the direction that a particular neuron likes, it will fire more action potentials. When it moves that opposite direction, it will fire fewer (permits the action to occur; inhibition is a big part of movement and important)

Complex movement requires primary motor cortex to do what?

contract multiple muscle synergists to different degrees 

What does the Non-primary Motor Cortex include?

Includes supplementary motor area and the premotor cortex. Both are anterior to the primary motor cortex in the frontal lobe (motor control is in frontal lobe) planning occurs in these areas

What is the Non-primary Motor Cortex involved in?

Broadly involved in motor planning (along with other areas), these regions prepare specific sequences of voluntary motion that are executed by primary motor cortex

What is the supplemental motor area?

is thought to generate motor programs for preplanned movement

What is the premotor cortex?

is thought to generate motor programs in reaction to external events (reaction; ball thrown at you and have to move to catch it and react; not reflexes) 

What is the Extrapyramidal Motor System?

Regulates the pyramidal motor system, in part via specific thalamic nuclei that project to primary and nonprimary motor cortex

What does the Extrapyramidal Motor System include?

Basal Ganglia: area of the forebrain that receives heavy dopamine input from the midbrain. Contains ‘Go’ and ‘Stop’ pathways for motion, that, when activated, initiate or halt behavior, respectively (important for getting voluntary motion going) 

Cerebellum: hindbrain region with more neurons than the cortex, semi-mysterious in function but known to contribute to precision motor control (has more neurons than your cortex; more dense; fewer glia)

How do the Basal Ganglia and Cerebellum talk to each other in the Extrapyramidal Motor System?

they influence motor cortices via largely parallel pathways through the nuclei of the ventral anterior and ventral lateral nuclei (together: VA/VL complex) of the thalamus (info is routed through distinct parts of VA/VL in order to influence motor cortex)

Many neurons in the striatum (part of the basal ganglia) express what?

either D1-like or D2-like dopamine receptors. The D1-like neurons generally send a ‘Go’ message when activated, whereas the D2-like neurons generally send a ‘Stop’ message (separate from each other; not overlapping) 

What does Dopamine do to the two receptors in the striatum?

Dopamine generally excites neurons that express D1-like receptors and generally inhibit neurons that express D2-like receptors. So the effect of dopamine release is usually to increase movement (removal of a stop signal and addition of a go motion)

What is Cerebellar agenesis?

a very rare condition in which the cerebellum never forms and in development (space remains but no tissue there); will lead to issues involved with walking and speaking (need a cerebellum to communicate language and smooth precise motions)

The nervous system is a computational instrument that

detects and analyzes environmental stimuli in order to guide the behavior of the organism that possesses it 

Specialized sensory systems detect and analyze environmental stimuli that come in the form of what?

1. Specific forms of energy (light, sound waves, etc)

2. Particular chemicals (odors, tastes)

The detection and analysis of these environmental stimuli allows your brain to do what?

build a representation of the world around you, without which you could not navigate the environment (how your brain creates an image of the world; not the actual world per say) 

What are receptor cells specialized for?

the detection of specific energies and chemicals in their environment (determine when certain stimuli are present and initiate the process; have to turn this into something our brain can understand=stream of action potentials)

What is sensory transduction?

The receptor cell converts this sensory input into an electrical signal that can be processed and interpreted by the nervous system

Once transduction has occurred, the sensory stimulus is encoded as

a stream of action potentials traveling toward the brain via the peripheral nerves

What are two examples of sense modalities that animals have but humans don’t?

1. Migratory birds use special receptor cells in their eyes to detect the Earth’s magnetic field. This allows them to navigate long distances (essentially a compass; a good cardinal point that is stable to rely on for navigation) 

2. Various species of fish create an electrical field in the water around them and use electroreceptors on the skin surface to detect when an object enters the field (can tell when something disrupts the field)

What is unique about sensory receptors between species?

Even if two species both possess a given sense, they may not be able to perceive all the same stimuli 

1. In other words, sensory receptors, even if they are designed to detect the same energy, can be tuned differently

What are some examples of sensory receptors being tuned differently?

1. elephants and cats can hear sounds that humans cannot (able to pick up more frequencies than we can) (older people cannot hear super high pitches than young people) 

2. The mantis shrimp has 12-16 different color-sensitive cells in its eye, while you only have 3 (compared to the mantis shrimp we are basically colored blind)

One sensory system can have multiple different types of receptor cell(related to each other but different; all touch but detect different things), which allow you to distinguish inputs that are what?

both qualitatively (different kind of input) and quantitatively different (different amount of input)

What’s an example of a qualitative difference in a sensory system?

you have different receptors in your skin for pressure and vibration and different receptors in your eye for different colors (qualitative differences)

What’s an example of a quantitative difference in a sensory system?

You also have different receptors in your eye that are sensitive to different light levels (quantitative difference)

What’s a receptive field?

the area within which a receptor cell can detect a stimulus

What does a receptive field often correspond to?

corresponds to an area of space (for instance, the patch of skin that will activate a particular touch receptor when pressure is applied to it)

1. However, your auditory system contains receptor cells that are activated by a range of sound frequencies. That frequency range is the receptive field for those receptors

What is sensory adaptation?

a progressive decrease in a receptor’s response to a sustained stimulus (putting a shirt on in the morning; receptors get used to the shirt being there all the time and stop responding)

Describe phasic receptors

Phasic receptors display adaptation (literally blind to the input until it changes again) 

1. The decrease in the signal coming in from a phasic receptor allows the brain to ignore an unchanging, harmless stimulus

Describe tonic receptors

Tonic receptors respond as long as the stimulus is present

Tonic receptors remind the brain that stimulus is still present, even if it isn’t worth much attention

Where does sensory information and perception occur?

Sensory information is detected by receptor cells in the periphery, but perception occurs in the brain

each sensory system has what associated with it?

primary sensory cortex associated with it (different patches of wrinkly processes each sense). In most cases, these regions of cortex receive sensory info from the thalamus 

1. Broadly speaking, the earliest stages of perception occur in the primary sensory cortex. Damage to primary sensory cortices can leave unable to consciously experience that sense (ex: stroke to auditory sensory cortex will deafen you)

Sensory cortex is highly organized, forming a what?

topographic map of the receptors that take in the information from the environment 

The somatosensory cortex processes what?

touch information, and has a map of the skin surface(extremely sensitive parts of your body; lots in hands and face; sensitive bits get a lot; nonsensitive gets less). For a given region of the body, receptive fields in neighboring areas of skin are processed by neighboring areas of the brain (somatotopic map)

The auditory cortex processes what?

sound information, and is arranged so that similar sound frequencies are processed by neighboring areas (tonotopic map) (not organized around space but frequency)

What are non-primary and association cortices?

they receive information from primary sensory cortex and integrate inputs from multiple senses (want the systems to talk to each other so need these to bridge) 

1. They can contain polymodal neurons that respond to multiple different forms of sensory information

2. Association cortices play a role in creating an integrated sensory world and in storing remembered information

What is a rare thing that can occur with multi-sensory processing?

may cause synesthesia, a condition in which a stimulus in one sense modality also causes a sensation in another (see color blue and certain smell is reminded every time you see it) when colors taste like something 

Sensory cortex can undergo what?

plasticity, or change as a result of experience

Describe the plasticity of a sensory cortex?

Extensive or highly skilled use of a body part can expand its representation in the somatosensory cortex (playing the violin-given more bandwidth for the hand that does the frets)

Conversely, loss of a limb can cause neighboring regions to take over the area associated with the lost part 

1. Plasticity has limits-individual who suffer strokes that impact somatosensory cortex can develop the delusional belief that a given region of the body no longer belongs to them (neglect syndrome-when you lose somatosensory cortex; your sense of your bodily self requires constant input being processed by this part of the brain so it fundamentally changes your sense of reality) (can lose an arm but still feel it; lose the part that senses it in the brain and then feel like it’s no longer part of you)

Where is the Primary Somatosensory Cortex located?

Located on the post-central gyrus in the parietal lobe (next to primary motor cortex which is precentral gyrus) these two areas need to talk to each other -basically laid out the same as well

How is the Primary Somatosensory Cortex laid out?

has a topographical map of the skin surface. The area of somatosensory cortex taken up by a region of the body is proportional to the number of receptors in that region (hands and face take up the most)

What are some of the variety of somatosensory receptors?

These include receptors specialized for: heat, cold, pain (tissue damage), pressure, texture, stretch (from motion of the limbs), etc

What else is the somatosensory cortex involved in besides touch information?

also involved in proprioception, or perception of the position of the limbs and body in space. This involves specialized receptors that detect stretch in tendons, contraction of muscles, and joint angle (can tell brain how contracted or relaxed muscles are)

What is the specific touch receptor example we need to know?

Pacinian Corpuscles

What are Pacinian Corpuscles?

Receptor specialized for sensing (not strong )pressure and texture. They are phasic receptors-they adapt quickly to a constant stimulus-cares about change; adapt quickly to the change and quiet down fast

1. Layers of connective tissue(onion like-stimulus has to be enough to actually exert pressure on the nerve) surround a nerve ending, which responds to inward pressure against these layers

What feature does a Pacinian Corpuscle nerve ending have?

The nerve ending has special mechanically-gated sodium channels that open when pressure causes the membrane to stretch (it physically pulls open the ion channels).

When the mechanically-gated sodium channels open when pressure occurs on a Pacinain Corpuscle nerve ending, what does it cause?

This causes a generator potential, which is like an excitatory postsynaptic potential caused by specific sensory input (instead of neurotransmitter release) neuron wants to fire an action potential in response to sensory input

Somatosensory receptors like the Pacinian corpuscle surround the nerve endings of neurons with cell bodies where?

in the dorsal root ganglia, which run along with spinal cord 

Describe the The axons of DRG neurons

they arise directly from these nerve endings. Thus, the summation of generator potentials is what determines whether or not an action potential is fired 

1. The action potential travels past the cell body in the DRG to axon terminals that form synapses in the CNS

What is a dermatome?

Each of the 31 pairs of spinal nerves is associated with a strip of skin that it collects information from

How are dermatomes organized?

These are roughly organized from superior to inferior so that higher regions of the spinal cord are collecting info from higher up in the body (series of levels; superior-takes in superior areas of the body)

Axons of DRG neurons travel up the spinal cord to where?

the medulla

DRG neurons form what when they get to the medulla?

form synapses on medulla neurons (have a synapse in the medulla)

What does the medulla do in response to the DRG neuron synapses on medulla neurons?

Medulla neurons send axons across the midline, forming synapses on neurons in the contralateral ventral posterior nucleus (VPN) of the thalamus. As a result, stimuli on the left side of the body are processed on the right side of the brain and vice versa (goes to thalamus(like a sensory switchboard))

Once sensory input is at the VPN, what does it do?

VPN neurons send axons to the primary somatosensory cortex (how info goes from sensory input to primary somatosensory cortex) 

Flavor is a combination of inputs from which multiple different senses?

1. Taste: gustatory, chemicals in food

2. Smell: olfactory, air born chemicals (food tastes worst when your nose is stuffed)

3. Somatosensory: texture (mouthfeel), pain (pain receptors in your tongue) (spiciness), temperature

What are Papillae?

are bumps on the surface of the tongue in which tastes buds and other sensory receptors are embedded (gustatory and sensory systems in here)

1. Papillae increase surface area and thus the number of sensory receptors 

2. They come in different types that are associated with different parts of the tongue.

What is the most common type of Papillae?

filiform papillae, do not contain taste buds and instead have somatosensory receptors (looks like a cartoon flame; pain and texture receptors) 

What are the 5 basic tastes that the tongue can identify?

1. Salty

2. Bitter

3. Sour

4. Sweet

5. Umami or savory

What are taste buds?

A collection of 50-100 taste receptor cells that all respond to one of the 5 basic tastes (many cells that care about one particular taste)

What do taste buds extend?

microvilli, hair-like extensions covered with taste receptor proteins, into the taste pore, an opening that connects the taste bud to the surface of the tongue

How do taste receptor cells communicate with nerve endings?

Many taste receptor cells release ATP onto the nerve endings of neurons that contribute to one of three cranial nerves (taste requires metabolic energy for it to work). This form of communication does not involve a well-defined presynaptic membrane-ATP release is not precisely spatially targeted (not a very small space with puff of chemical; it gets picked up by nerve endings eventually)

What’s the life span of taste receptor cells?

life span of roughly 10-15 days

NaCl (salt) dissolves into what?

into Na+ and Cl- in the saliva

Taste receptor cells that respond to salt have what?

sodium channels that allow Na+ into the cell (allows sodium to enter the cell directly, open all the time)

How does the sodium from the salt you taste turn into a message your NS can understand?

Thus, sodium from the salt that you taste enters receptor cells and contributes to a generator potential directly, depolarizing the cell. This opens voltage-gated Ca2+ channels, which triggers ATP release (the food itself literally becomes the message the NS comprehends)

Describe the sour taste

IS acidic 

Acidity is determined by the concentration of hydrogen (H+) ions in a substance. Acidity is measured using pH, which is on a scale of 0-14 (acid is low). Limes have a pH of -2.4

1. Taste receptors that respond to sour have hydrogen channels that allow H+ ions into the cell. Like sodium channels in the case of salt, this creates a generator potential that depolarizes the cell and leads to ATP release

What are the notably substances that elicit sweet?

sugars like sucrose and fructose (naturally high in fruits)

What receptors bind to sugars and other sweet-tasting chemicals?

T1R receptors, of which there are multiple types, bind to sugars and other sweet-tasting chemicals 

When T1R receptors bind to sugars what is formed?

When they bind to sugars, the receptors then bind to each other (find other T1R to bind to), forming a dimer (a compound molecule made of two similar or identical subunits)

Dimerized T1R receptors activate what?

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

Umami (savory-meat flavor) taste is caused by what?

glutamate and other amino acids

Glutamate binds to metabotropic glutamate receptors on taste receptor cells, activating what?

activating G-proteins on the inside of the cells, depolarizing them, and leading to ATP release (same molecule doing a slightly different thing)

Describe Bitter taste

An extremely wide range of chemicals cause bitter taste (lots of bitter make you stop eating; don’t eat that reaction) 

1. They all bind to T2R receptors, of which there are 2-3 dozen types (can respond to lots of different chemicals). These also activate G-proteins, which depolarizes receptor cells and causes ATP release 

Describe the Gustatory Pathway

Taste receptor cells release ATP onto the nerve endings of neurons with cells bodies in the ganglia of 3 cranial nerves (don’t need to know which cranial nerves these are) 

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(beneath the temporal lobe; hidden by the thumb of the boxing glove) and parietal lobe

*Unlike other sensory pathways, the gustatory pathway is what?

ipsilateral-meaning taste input from the left side of the tongue is processed on the left side of the brain (doesn’t cross at the midline; left does left; right does right) 

Smell (olfaction) involves what?

airborne molecules that are drawn into the nasal cavity when you breathe (float in air and breathe in) 

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

Olfactory Receptor Cells are located where?

Located in the olfactory epithelium(means a layer of skin), which covers ~5 square cm within the nasal cavity in humans

How are olfactory receptor cells specialized?

Olfactory receptor cells are specialized neurons with a dendrite that branches into cilia on the surface of the olfactory epithelium. Cilia are covered in olfactory receptor proteins (they do action potentials that the CNS receives but they have cilia NOT dendrites)

What does each olfactory receptor cell express?

Each receptor cell expresses one type of receptor protein (which can be activated by multiple odor molecules). In humans, there are ~400 types of receptor protein. In mice, there are ~1000

Olfactory receptor proteins activate what?

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

Olfactory receptor cells send axons a short distance through holes in the skull to what?

the nearby olfactory bulb, a small structure in the central nervous system. This short trip is the entire length of the olfactory nerve, one of the cranial nerves

Olfactory receptor cells axons form synapses where?

in the glomeruli (singular glomerulus) of the olfactory bulb. Glomeruli are areas of synaptic connectivity that contain the axons of olfactory receptor cells and the dendrites of mitral cells (what receives the input from olfactory cells), neurons that carry olfactory information elsewhere in the brain 

Each glomerulus receives input from

olfactory receptor cells expressing one specific olfactory receptor protein (dedicated to input from cells with one receptor; one smell goes to one receptor)

What is unique about the olfactory pathway?

*Olfactory information makes it to the cortex without passing through the thalamus (mitral cells directly send it to the cortex directly)

Where can mitral cells directly project?

Mitral cells can project directly to the primary olfactory cortex in the temporal lobe, as well as to the amygdala, a region important for emotion 

Primary olfactory cortex contains an

olfactory map-information from each glomerulus is processed by its own distinct chunk of cortex (each glomeruli gets a specific part of the cortex to activate)