PHSL231 Progress test 2

sensory receptors of the skin

converts physical stimulus to action potentials in primary sensory neutron

types of sensory receptors

-thermoreceptors
-position of limbs
-touch receptors
-pain (nociceptors)

thermoreceptors

-different types are more active at warm or cold temperature ranges
-responsive to changing temperature

proprioceptors

-position of limb receptors
-muscle spindles, golgi tendon organs, joint capsule, skin mechanoreceptors

touch receptors

-sensitive to mechanical deformation
-various types

pain receptors (nociceptors)

-respond to extreme mechanical stimuli, temperature and/or chemical stimuli
-receptors are axon endings without obvious anatomical specialisations
-found everywhere in the body except the brain

skin touch receptor

-high density of receptors in glabourous /finger print skin
-receptor fields are small
-can orientate receptors in certain directions to detect whether skin is being moved

pacinian corpuscle

-skin receptor
-detects pressure and vibration
-when the membrane is stretched receptors are deformed causing influx of Na+-\> depolarisation -\> generation of AP at 1st node of ranvier
-membrane potential quickly recovers as receptors are rapidly adapting
-can only tell when something is staring

sensory coding- modality

-specificity of receptors
-eg touch verse temperature

sensory coding-intensity

-frequency of AP's in each axon
-number of axons activated

sensory coding- location

-mapping of receptive fields of individual primary afferents to specific cortical locations
-somatotopic representation

sensory coding- duration

-rapidly adapting receptors respond briefly even if the stimulus is sustained
detect movement , changing pressure
-slow adapting receptors signal true duration of stimulus

anteriolateral/ ventral spinothalamic pathway

-axons cross low in the spinal cord
-pathway for pain and temperature
-general and broad sensation

dorsal column/medial lemniscus pathway

-axons cross in medulla
-pathways for fine touch and proprioception
-detailed information for generating motor output

lateral inhibition

-increases the accuracy of sensory information
-mediated by inhibitory neurons
-localises senstation to a restricted area of the skin
-used when location of a stimulus is required or where a pattern of input needs to be discriminated

primary somatosensory cortex

-ordered representation of the body
-area in cortex is proportional to density of receptors in that area of the body
-margins of representations are modifiable (plastic)

types of pain nerve fibres

1. "c" fibres
2. "As" fibres

"C" fibres

-smallest diameter
-unmyelinated axons
-slow conduction velocity
-signals ongoing damage (or potential damage)
-polymodal

"As" fibres

-small diameter
-myelinated axons
-faster conduction velocity
-signal acute onset of painful stimulus
-primarily mechanoreceptors

hyperalgesia

-when pain pathways become more sensitive
-can occur following injury or inflammatory disease (e.g. arthritis)
-due to sensation of sensory endings by locally released factors that cause changes at CNS synapse

inhibition of pain pathways

-inputs from nearby non-pain nerves inhibits responses of ascending pain fibres (i.e non painful flood the "gate" leading sensation of pain so there is a decrease in pain felt)
-e.g rubbing affected area, trans-epidermal nerve stimulation

endogenous opiates

-released at synapses on pain pathway neurons
-"natural analgesia" system, acute response to pain, stress
-site of action for centrally acting pain killers (morphine, codeine)

Endocannabinoids

-synthesised and released by neurons (but stored in vesicles)
-decreased long term sensitivity to pain
-act on pain receptors as well as centrally

interpretation of pain depends on

-arousal
-placebo
-anxiety
-association
-suggestion

referred pain

-feeling from viscera referred to the body surface
-e.g. heat pain to the neck and arm activated by stretch, ischema
-persumed to be due to "cross talk" of visceral and somatic sensory pathways

neuropathic/neurogenic pain

-nerve compression can cause pain to be felt in the region of nerve termination
-e.g pain in leg from compression of nerve in back by "slipped disc"

phantom limb

sensation felt in region that no longer exists
two causes
-ongoing activity in nerves that used to come from that part
-invasion of cortical representation for that part by intact body regions

Afferent division of PNS

-somatic sensory
-visceral sensory
-special sensory
-endocrine

Efferent division of PNS

-somatic motor
-endocrine
-autonomic motor (sympathetic, parasympathetic ,enteric)

ANS sympathetic

-widely distributed (salivary glands, eye, skin,viscera, muscles)
-first synapse in paravertebral and prevertabral ganglia
-post ganglionic fibres innervate organs
-except adrenal medulla supplied by preganglionic sympathetic Ach fibres direct from CNS, releases NE and E

ANS parasympathetic

-distributed less widely to viscera (mainly via vagus nerve), salivary glands, eye
-first synapse is in or near the target organ

Enteric nervous system (ENS)

consists of submucosal plexus and the myenteric plexus
-multiple neurotransmitters and receptors
-responds to local chemical and mechanical stimulation
-regulate motility, secretion and endocrine signalling through local reflexes
-activity is autonomous but is influenced by parasympathetic (incr.) and sympathetic (decr.)

Ach released by enteric motor neurons

-excites smooth muscle via muscarinic AChRs
-excites secretion via nicotinic AChRs

vasoactive intestinal peptide (VIP)

-inhibits smooth muscle in the enteric nervous system
-has no effect on control of secretion

local ENS reflexes

sensory neurons receive input from stretch and serotonin (released for enerochromaffin cells in the mucosa layer)
-synapse on to interneurons in the myenteric plexus which synapse onto inhibitory motor neurons causing anal relaxation
-synapse onto interneurons in the submucosal plexus which synapse onto excitatory neurons in causing oral contraction

spinal cord

-processing commands from the brain
-reflexes (stretch, tension )
-rhythmic motor patterns (eg locamotion, chewing)

Stretch reflex

maintains length
-muscle spindle (tracts resting length of the muscle) is activated, contraction of that muscle

tension reflex

maintains force
- golgi tendon organ on muscle activated causes contraction of opposite muscle

withdrawal reflex

ipsilateral (same side as stimulus)
-flexors active, extensors relaxed
-limb withdrawn
contralateral (opposite side of the body)
-extensors active, flexors relaxed
-takes weight to maintain balance

central pattern generators

spinal cord and brain stem generate basic patterns of rhythmic muscle activity (e.g locomotion)
- commands from the brain start/stop and regulate speed force and direction

rhythmic muscle activity examples

locomotion
breathing
chewing
swallowing

primary motor cortex

-ordered map of the body
-regulates spinal cord motor systems (via corticospinal tract
-body parts are represented roughly sequentially across the cortex
-area devoted to each part is dependant on the level of fine control and/or the extent of use

cortocospinal pathway

-output from motor cortex control spinal neurons for fine, isolated movements (crosses to opposite side)
-most input is to interneurons

Brain stem pathway

coordinated activity in large muscle groups for posture , locomotion, routine activities (crossed and uncrossed)

special roles of the primary motor cortex

-controls force of muscle contractions (greater rate of neural activity, greater force)
-controls direction of movements (relative activity of many cortical neurons, controlling muscles each side of the joint controls direction of movement
-axons synapse directly onto alpha motor neurons (not interneurons) for fast direct effects

Claudia mitchell bionic arm

-redirected the nerves to the patients chest muscles
-when she 'thinks' about a specific movement of the arm and hand the nerve impulses travel from the brain to the corresponding location on the muscle
-electrodes fixed to the harness direct electrical impulses emitted from the muscle to the arm
-enables arm to perform movements

roles of the basil ganglia

-monitors and helps plan cortical activity involved in movement
-helps cortex select combinations/sequences of muscle activation
-postive feedback to cortex for selected activity
-needed for initiation of movement
-dopamine input form substantia nigra vital to allow for proper functioning

Parkinsons disease

-death of dopamine neurons
-difficulty benigning movements, slowed movements, tremor
-cause uncertain, genetic and environment, truma

treatment of parkinson disease

-dopamine replacing drugs (precursors for dopamine taken up and released by surviving substantia nigra cells
-deep brain stimulation
-possibly transplantation of dopamine cell

cerebellum

-basic circuit repeated millions of times
-resembles masssive 'parallel processor' (as it recieves both sensory information and info from the brain)

roles of the cerebellum

-helps plan execute and learn motor programs
-intergrats sensory information with planed motor programs
-organises timing of individual muscle contractions around joints
-compares the intended result of planned movement with the actual result and modifies ongoing activity
-may also be used by other brain stems

cerebellar injury

-results in movements that are slow and uncoordinated
-individuals with cerebellar lesions tend to sway and stagger when walking

damage to cerebellum symptoms

-loss of co-ordination of motor movements
-inability to judge distances and when to stop
-inability to perform rapid alternating movements
-movement tremors
-staggering wide based gate
-tendency towards falling
-weak muscles
-slurred speech
-abnormal eye movements

EEG

-electroencephalogram
-measures brain activity

EEG function

-used to monitor behaviour state (coma, sleep stages)
-diagnose epilepsy
-localise brain areas active in different tasks

Alpha rhythm

more prominent in individuals has eyes closed and is relaxed

beta rhythm

more prominent in alert state

SWS

-decreased eye movement (EOG)
-increased muscle movement (EMG)
-decreased heart rate
-decreased respiration

REM sleep

-increase eye movement (EOG)
-decreased muscle movement (EMG)
-increased heart rate
-increased repiration

sleep/wake cycle

-basic rhythm generated by clock in hypothalamus called suprachiasmatic nucleus
-accurate entrainment to day length via input from the visual pathway

orexins

proteins released by neurons in the hypothalamus needed to keep us awake

reticular formation

-region in the pons involved in regulating the sleep-wake cycle
-neurons active when awake
-reduced activity when asleep

functions of sleep hypotheses

-recuperation
-energy conservation (evolutionary adaption)
-memory consolidation
-allows for dreaming

consciousness definition

able to immediately respond to the environment

unconsciousness definition

sleep: able to be roused complex pattern of brain states
coma: unable to roused disordered brain state
vegetive state: sleep cycles but no return to consciousness

schizophernia

-disorder of thinking- psychosis
-thought to be related to dopamine system
-treatment of drugs that decrease dopamine transmission

postive symptoms of schizophrenia

-hallucinations
-delusions
-paranoia

negative symptoms of schizophrenia

-social withdrawal
-apathy
-catatonia (state of apparent unresponsiveness to external stimuli)

disorders of mood

depression
SADD
bipolar

Depression

-persistent sadness, apathy, feeling of hopelessness
-endogenous arise without apparent life event harder to treat
-reactive in response to life event
-thought to be related to serotonin system
-treatment of drugs that increase serotonin levels
-cause unknown

SADD

-seasonal affective depressive disorder
-anual depression

bipolar

-depression alternates with mania
-mania elavated mood, high energy, grandiosity, poor judgment, delusions
-cause unknown
-treatment of lithium, anticonvulsants may smooth out fluctuations in neuronal excitability
-likely to be a network problem involving communication links

contralateral neglect

-neglect one side of visual world
-disorder of consciousness

prefrontal cortex executive functions

-planing
-emotional control
-moral judgement

types of memory

-declarative
episodic
semantic (words and their meanings, people, faces, concepts)
-procedural
memory of how we do things

declarative memory brain activity

STM
hippocampus and other temporal lobe structures
LTM
many areas of association cortex

procedural memory brain activity

STM
widely distributed
LTM
basal nuclei, cerebellum and premotor cortex

STM

-continuous activity in brain circuits
-if activity is interrupted memory is lost

LTM

-more permanent changes in brain functions
-probably involves long term changes in strength on specific synapses

transfer from working memory to LTM is enhanced by

-high emotional impact
-importance for survival
-repetition
-processing, forming new combinations linkage to existing knowledge

hippocampus

-located in the medial temporal lobe of the brain
-important role in long term memory storage
-damage reduces ability to form new memories

brocas area

-left frontal lobe
-involved in constructing motor output of language

wernicke's area

-left temporal lobe
-involved in processing language meaning both input and output comprehension

left brain function

analytical
verbal

right brain function

-intuitive
-space perception
-music
-primitive language ability

visible spectrum of wavelengths

400-750nm

eye function

detects light and processes visual information to create visual perceptions and guide behaviour

eye components

optical component
-for collecting and focusing light into the plane of the retina
neural component
-converts energy of light onto patterned changes of membrane potential that other part of the brain use to generate visual perceptions

labelled eye

passage of light into the eye

light from object-\> cornea-\> aqueous humor-\> pupil-\> lens-\> viterous humor-\>retina fovea

refraction

when light travels from a medium of one refractive index to a medium of another causing a change in direction of light

refractive power

-the ability of lens to bend light
-measured in diopters
-reciprocal of focal length in meters

relaxed eye refractive power

60 diopters

3 omponents of the near response

1. accommodation
2. constriction
3. convergence

accommodation

-contraction/relaxation of ciliary muscles to alter less shape and change refractive power

distant vision

-low parasympathetic activity
-cilary muscles relaxed
-zonula fibres taut
-lens is flattened
-very little refractive power

near vision

-parasympathetic activation
-cilary muscles contract
-zonular fibres relax
-lens becomes round
-increased refractive power

constriction of pupil

-improved depth of focus
-fewer optical aberrations

convergence of eyes

allows objects remain in register on corresponding parts of the two retina via extra ocular muscles

emmetropia

normal vision