bio 1191 ch. 16

what is a sensation vs perception

sensation

• a conscious or unconscious awareness of an internal or external stimuli

perception

• the conscious awareness and interpretation of a stimuli

what does the nature if a sensation + type of reaction depend on?

it depends on destination of the input

• spinal cord = reflexes

• brain stem = more complex reflexes (heart rate, respiratory rate)

• cerebral cortex = conscious awareness of the stimulus

are are the 3 thigns perception involves

#1: cerebral cortex

#2: precise localization + indentification

#3: memories of our perceptions, which are stored in the cerebral cortex

what are some examples of sensation

• baroreceptors

• chemoreceptors

• nociceptors

• thermoreceptors

what are stimuli we are not aware of?

• x rays

• high frequency sound waves

• UV light

can we have sensations that are not perceived? give examples

yes

• blood oxygen saturation levels

• amount of a specific hormone (eg: insulin)

• neuroreceptors

what is a sensory modality

a specific type of stimuli

• eg: pain, temp, touch, vibration, hearing, vision

explain receptor specificity

when a particular sensory neuron carries information for only one sensory modality = receptor specificity

what are the 2 classes of sensory modalities

#1: general senses = visceral and somatic sensations

#2: special senses = smell, taste, vision, hearing + equilibrium

explain the 4 steps of the process of a sensation

#1: stimulation of a receptor

• can be dendrites of a neuron or a specialized cell

• exhibit selectivity = only respond to one type of stimuli

• stimulus must be in the receptive field

#2: transduction

• conversion of a stimulus into a graded potential (electrical signal)

• amplitude of the graded potential depends on the strength of the stimulus

• NOT propagated

#3: generation of impulses

• if the graded potential reaches threshold, impulses are generated and sent to the CNS

#4: integration

• the integration of sensory input by the CNS (cerebral cortex is responsible for the perception of sensations)

whar are the 3 types of classifications for sensory receptors

• structural classification

• location of receptors + origin of stimulus

• type of stimuli they detect

how does a sensory receptor respond to a stimulus?

by generating a receptor potential, graded potential that leads to either….

• release of neurotransmitters

• generation of a nerve impulse/ AP

the amplitude of the receptor potential varies with the intensity of the stimulus, and the frequency of nerve impulses or neurotransmitters reflects the strength of the stimulus

free nerve endings desc + stimulation detetced

• detects: itch, tickle, temp, pain, light touch + smell

• bare dendrites

encapsulated nerve endings desc + stimulation detetced

• dendrites enclosed in a CT capsule

• detect pressure, vibration + deep touch

separate receptor cells desc + stimulation detetced

• specialized cellsthat respond to a stimulus by releasing NT’s, which synpase with first order neurons

• vision, taste, hearing

exteroreceptors

• receptors located near the surface of the skin, detect external stimuli

• eg: vision, hearing, smell touch, taste, pressure, pain, external temp

interoreceptors

• located internally and monitor the internal environment

• eg: blood volume, muscles, nervous system

propioreceptors

• located in musles, joints, tendons, inner ear

• detect body position, movement + equilibrium

what do mechanoreceptors detect + examples

detect mechanical stimuli

• eg: deformation, stretching, bending, touch, pressure, BP, vibration

what do chemoreceptors detect

detect molecules

• eg: taste, smell, changes in body fluid chemistry

what do osmoreceptors detect

detects osmotic pressure in fluids

what is adaptation in sensory receptors? what does it result in

this is the tendency for receptor potentials to decreae in amplitude during a maintained, constant stimulus

• due to receptor adaptation, the perception of a stimulus may fade or disappear even though the stimulus persists

what are the 2 types of sensory receptor adaptation

rapidly adapting receptors (smell, touch, pressure)

slowly adapting receptors (pain, propioreception)

• nerve impulses continue as long as the stimulus persits, pain is not easily ignored

what are somatic sensations the stimulation of?

stimulation of sensory rceptors in the skin, mucous membranes, muscles, joints, tendons

describe the distribution of our sensory receptors

sensory receptors are unevenly distributes throughout the body, with the highest density being in the fingertips, lips, and tongue

what are the 4 somatic modalities

• tactile

• proprioceptive

• pain

• thermal

tactile sensation examples + receptors

touch pressure, itch, tickle, vibration

• tactile corpuscles (messiners corpuscles)

• hair root plexuses

• free nerve endings

• nonencapsulated corpsucles

• bulbous corpuscles

• lamellar corpuscles (pacinian)

which two of the tactile receptors are rapidly adpatping + describe them

#1: tacticle corpsuscles

• dendrites enclosed in CT

• located in the dermal papillae

• detect touch, low frequency vibrations

• rapidly adpating

#2: hair root plexuses

• free nerve endings located arund hair follicles

• detect the movement of hair

• rapidly adapting

which two of the tactile receptors are slowly adpating + describle them

#1: bulbous corupscules (ruffini’s)

• enclosed in CT

• located in the dermis, ligaments and tendons

• detect stretching, pressure, + continuous touch

#2: non-encapsulated sensory corpuscles

• free dendrites touching cells of the stratum basale

• continuous touch + pressure

• 25% of receptors in the hands

• slowly adapting

what is pressure

pressure is a sustained sesntation felt over a larger area than touch

• deforms deep tissue

pressure is longer lasting and has less variation in intensity than touch

what are the receptors for pressure

• non- encapsulated sensory corpuscles

• bulbous corpuscles

what are vibration sensations a result of?

vibration sensations are a result of rapidly repetitive sensory signals from tactile receptors

what are the 2 receptors for vibration?

• tactile corpuscles - detect low frequency vibration

• lamellar corpuscles - detect high frequency vibrations

describe lamellar corpuscles

• dendrites are enclosed in a CT covering

• located in the subcutaneous tissues + viscera

• detect deep pressure + high frequency vibrations

• rapidly adapting

what receptors detect itch and tickle? what stimulates these sensations?

free nerve endings found in skin

• itch and tickle are stimulated by inflammation + chemicals (histamine, mosquito saliva)

what receptor detects thermal sensations

free nerve endings in the skin/ mucous memebranes detect thermal sensations

cold receptors vs warm receptors

cold receptors

• located in the stratum basale, respond to temps between 10-35 degrees celcius

warm receptors

• located in the dermis, respond to temps between 30-45 degrees celcius

• both adapt at first, but continue to generate nerve impuleses at a low frequency

why do you feel pain when you touch something very hot or very cold

because when you touch something below 10 degrees or above 45 degrees, you stimulate pain receptors instead of thermal receptors

why are pain sensations important? give examples of things that cause pain

pain is a sensation that is necessary for survival, it indicates tissue damaging conditions

• stretching, prolonged muscle contraction, muscle spams, ischemia

pain adaptation is slight, if at all

what does tissue injury result in?

tissue injury results in the release of chemicals that stimulate nocicpecotrs

• eg: postaglandis

pain may still persist after the stimulus is removed, because the chemicals stimulating nociceptors are still present

slow pain vs fast pain

fast pain

• sharp, acute, prickling pain (needle)

• occurs rapidly after stimulus (0.1 sec)

• easily localized, not felt in deeper tissues

• travels thorugh medium diameter, myelinated nerve fibers

slow pain (chronic)

• aching, burning, or throbbing pain (toothache)

• begins more slowly (1 sec) and increases in intensity

• easily localized, but pain is diffused across a larger areas

• travels through small diameter, unmyelinated nerve fibres

what does superficial somatic pain stimulate

stimulation of pain receptors in skin

what does deep somatic pain stimulate

• stimulates pain receptors in muscles, joints, tendons

what does visceral somatic pain stimulate? describe the 2 types of distension

• stimulates pain receptors in visceral organs

• localized damage may cause no pain, but diffused visceral stimulation can be severe (result of swelling or ischemia)

• distension of a bile from a gallstone

• distension of a ureter from a kidney stone

what is an example of referred pain?

a heart attach can be felt in the skin along the left arm since both the heart and left arm are served by the same segment of the spinal cord; T1-T5

in referred pain, where is visceral pain usually felt

usually felt in the skin overlying the stimulated organ, or in a surface area far away from the organ

• it can be difficult to identify the exact location

• skin area and organs are served by the same segment of the spinal cord

what are the 3 types of analgesic action

#1: can block the formation of chemicals that stimulate nociceptors

• eg aspirin and ibuprofen block the formation of prostaglandins

#2: block the conduction of nerve impulses along pain fibres

• eg: norocaine = local anesthetic, blocks voltage gates Na+ channels

#3: can lessen the preception of pain by the brain

• pain is sensed but not percieved as noxious

• morphine binds to the same receptors of endorphins and dynorphins, inhibits substance P

what is propioception, give examples, what does it allow us to gauge? do propioreceptors adapt?

the awarness of body postion

eg: walking, getting dressed, typing without looking

• aloows us to estimate the weight of objects ( so adjustment to force can be made)

• propioreceptots adapt slightly

where is propioreceptive information sent?

to the cerebellum and cerebral cortex

where are receptors for propioreception located?

• golgi tendon organs

• muscle spindles

• joint kinaesthetic receptors - bulbous (pressure) + lamellar corpuscles (accelleration/ deacceleration)

where do somatic sensory pathways carry information from and to

carry information form somatic sensory receptors to the primary samatosensory area of the cerebral cortex and the cerbellum

first order neuron vs second order neuron vs third order neuron

first order neuron

• carries info from the somatic receptors to the brain stem or spinal cord

second order neuron

• carries impulses from brain stem/ spinal cord to the thalamus

third order neuron (deuccsates)

• carries impulses from the thalamus to the primary samatosensory area of the cortex (on the same side)

what are the 3 somatic sensory pathways

• posterior column medial lemniscus pathway

• anterolatral spinothalamactic pathway

• trigeminothalamactic pathway

how are samatosensory signals carried to the cerebellum

axon collaterals of somatic sensory neurons carry signals into the cerbellum

why do somatic sensory neurons send axon collaterals to the cerbellum

to provide sensory input that is essential for…

• posture

• balance + coordination of skilled movements

what are the 2 major routes for propioreceptive signals to reach the cerbellum

anterior spinocerebellar tract

posterior spinocerebellar tract

note: no decussation (signal travels up to the same side of the body)

what does a somatic motor pathway always involve?

alwyas involves 2 motor neurons in a series

upper motor neurons vs lower motor neurons

UMN

• located in the cell bodies of the CNS motor area

LMN

• extend from the brain stem or spinal cord and innervates skeletal muscles = final common pathway

in the somatic motor pathway, what structures does the control of body movement involve?

#1: motor portions of the cerebral cortex

• initiate + control precise movements

#2: basal nuclei

• maintains muscle tone + integrates semivoluntary automatic movements

#3: cerebellum

• fine tunes movements + maintains posture and balance

what is the function of the neural circuits

participate in the control of movement by providing input to the lower motor neurons

neural circuit

• lower circuit neurons location

located close to the lower motor neuron cell bodies in the brain stem + spinal cord

neural circuit

• local circuit neurons fucntion

local circuit neurons and lower motor neurons receive input from the upper motor neurons

neural circuits

• neurons of the basal nuceli

neuorns of the basal nuclei provide input to the upper motor neurons

neural circuit

• cerebral neurons function

cerebral neurons control the activity of the upper motor neurons

what are the 2 types of upper motor neuron pathways? decribe them

direct motor pathway

• provides inpit to lower motor neurons via axons that etend directly from the cerbral cortex

indirect motor pathway

• provides input to lower motor neurons from the motor centers in the brain stem

• includes synpase from basal nuclei, thalamus, cerbellum + reticular formation

where is the primary motor area located? function?

precentral gyrus of the frontal lobe

initiates motor voluntary motor movements via the upper motor neurons

what do upper motor neurons do

initiate voluntary movements

what is the function of the premotor area

it recieives input from basal nuclei and thalamus with the filtered inputs from the association areas of the cortex and it makes a motor plan; muscles, force, order of contraction

Why do some muscles have more motor cortex area devoted to them?

Because muscles with more motor units require more cortical area for fine control (e.g., fingers, tongue, lips, vocal cords)

what pathways are indirect pathways?

all motor pathways are indriect pathways except..

• medial + lateral cortiocospinal pathway

• corticobulbar pathway

what are the 5 major tracts of the spinal cord

UMN’s descend from the motor nuclei in the brian, thorugh the brain stem to the spinal cord where it goes thorough 1 or 5 major tracts of the spinal cord, where it then synapse with local circuit neurons and LMN’s

#1: rubospinal - from the red nucleus (midbrain)

• allows for precise movement of a distal part of a limb

#2: tectospinal - superior colliculi (midbrain)

• allows for the movement of the head and eyes in response to visual stimuli

#3: vestibulospinal - vestibular nucleus (CN III, pons + medulla)

• posture and balance

#4: medial and lateral reticulospinal - reticular formation

• maintains posture and balance during ongoing body movements

what are the 4 main functions of the cerebellum

• learning

• preforming skilled, coordinated movements

• posture

• equilibrium

what are the 4 ASPECTS of cerebellar function

#1- montiors the intention of movements

#2: - monitors the actual movement

#3: - montiors the intention of the movement with the actual movement

#4: provides corrective feedback

what are the 3 integrative function of the cerebrum

1- memory and learning

2- language

3- consciousness

what are the 4 characteristics of higher order function of the cerebrum

• preformed by the cortex

• interconnection between the inside and outside of the cortex

• involved cocious and unconcious processing

• subject to modification and adjustments

what is sleep

sleep is an altered state of conciousness or a state of partial unconciousness where the subject can still be aroused by certain stimuli

activity of the cortex during wakefullness vs sleep

during wakefulness, the cortex is very active

during most stages of sleep, the. cortex is less active

what part of the brain control sleep and wakeullness?

• what kind of function is it?

sleep and wakefulless are both integrative functions

• the reticular activating system (RAS) controlls sleep and wakefullness, and also had numerous other connections to the cortex

what happens to the RAS during arousal?

increased activity of the RAS leads to increased arousal

• when the RAS is activated, so is the cerebral cortex, which leads to arousal

the result of this is a state of wakefulness called consciousness

what types of input can activate the RAS

light, noise, pain, touch, but NOT smell

what is the activity in the RAS during sleep

• what is a chemical that reduces the activity of the RAS

very low activity

• Adenosine is a sleep inducing chemical in the brain that inhibits the activity of the RAS

how does tea and coffee keep you awake

caffine and theophylline (in tea), binds to adenosine receptors, therefore preventing adenosine from inducing sleep

NREM vs REM

non rapid eye movement sleep (NREM)

• inactive brain, active body

rapid eye movement sleep

active brain, inactive body

what are the 4 stages of NREM sleep

• makes up what % of total sleep time

NREM sleep makes up 75-80% of out total sleep time

stage 1

• person is drifiting off with thier eyes closed

stage 2

• light sleep

stage 3

• relaxed, with moderate sleep

• BT + BP have dropped

• 20 mins after falling asleep

stage 4

• deep sleep

• low brain metabolism

• reflexes and muscle tone intact

• stage in which bed wetting and sleep walking occur

describe the sleeo cycle thorughout the night

cycle of sleep = 1 > 2 > 3 > 4 > 3 > 2 >1

• REM = 90- 110 mintues

• with more 3-4 stages earlier and longer

• - REM sleep is later in the night

during what type of sleeo do our dreams occur

most dreams occur during REM sleep

how ,many episodes of REM are there in a 7-8 hour sleep cycle?

• how does it chnage throught ones sleep cycle

there are 4-5 episodes of REM in a 7-8 hour sleep

• episodes increase in length (first = 10 mins, last = 50 mins)

describe how REM sleep decreases with age

infant = 50% REM sleep

2 year old = 35% REM sleep

adult = 25% REM sleep

when is neuronal activity and oxyegn use highest?

during REM sleep

what happens to motor neurons uring REM sleep? why is this important

motor neurons are inhibited during REM sleep (except for breathing muscles + eye movements)

• paralysis of skeletal muscles during REM sleep us thought to be important for brain development

what is a coma? what casues a coma? what is recovery based on?

a coma is a state of unconsciousness with little to no response to stimuli

• casued by head injury, damage to the RAS, infection or drug/ alcohol overdose

• recovery is based upon the severity of damage

• you still have brain waves, therefore not brain dead

what is learning? what is memory?

learning is the ability to quire new information or skills through instruction or experience

memory is the process for which that information is stored and retrieved

what are the two main types of learning?

associative learning - linking 2 stimuli

• Palov’s dogs learning to connect the sound of a bell to food

nonassociative learning- learning through repeated exposure to a stimulus

what are the 2 types of non associative leanring?

habituation

• reponse gets weaker with repetition

sensitization

• response gets stronger with repetiton

short term memory vs long term memory

short term memory

• holds a few pueces of information for seconds to mintutes

long term memory

• holds onto important pieces of information for days or years

what is declerative memory? where is it stored?

things you can describe verbally

• names, places, events, facts

stored in the relevant cortical association area

what is procedural memory? where is it stored?

stores information about motor skill and routines

• riding a bike, dancing

• stored in the cerebellum, basal nuclei and premotor area

what is the function of the hippocampus in memory

• forms new declerative memories and then moves it to the cerbral cortex for long term storage

what is memory consolidation? what helps consoldation?

the process that turns short term memories into long term memories

• repetition helps consolidation (why studying over time works better than cramming)

how does the brain chnage use

changes use through plasticity

• meaning synapses and neurons can strengthen or weaken