Integration of physiological systems PDF

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06/10/ Motor control Motor control- generation of signals to coordinate contraction for movement or posture.Movement- transition between two postures.Threshold potential in motor neurones is -50mV.Depolarisation- sodium channels open and sodium enters.Repolarisation- sodium channels close, potassium...

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06/10/17 1. Motor control Motor control- generation of signals to coordinate contraction for movement or posture. Movement- transition between two postures. Threshold potential in motor neurones is -50mV. Depolarisation- sodium channels open and sodium enters. Repolarisation- sodium channels close, potassium channels open, potassium leaves, return to resting potential. Hyperpolarisation- ATP dependent sodium/potassium pump goes against the concentration gradient to restore resting potential.

α motor neurones- are large in diameter, go from the spinal cord --> skeletal muscle. A motor unit is an α neurone and all the muscle fibres it stimulates. Fine control- few fibres (eyes). Gross control- many fibres. λ (gamma) motor neurones- are smaller and synapse with intrafusal muscle fibres (striated) that are sensory organs to detect and provide feedback on strength of muscle contraction. Glutamate- excitatory- binds to NMDA ligand gated ion channel so it opens and allows positive ions in (Na+ and Ca2+).

GABA- inhibitory- binds to GABAA ligand gated ion channel so it opens and allows negative ions (Cl-) in. It will need more stimulus to reach the threshold, it can shorten the duration of an action potential. Reflex arc. No signal to the brain. Sensory/afferent neurone- from muscle to spinal cord. Hit the patella- stretching of quadricep- activation of sensory neurone- release of glutamatesynapses at α neurone to go to the quadricep- excitatory- AcH released, muscle contracts. Hit the patella- stretching of quadricep- activation of sensory neurone- release of glutamatesynapses at GABA interneurone- inhibitory- α neurone to the hamstring- no AcH, muscle relaxes.

09/10/17 2. Movement Stages- think, identify the target, place target in 3D, calculate trajectory of intercepting limb, calculate the force needed to exert on the limb. Brain areas- frontal lobe for skeletal muscle movement- includes primary motor cortex and premotor cortex. Parietal lobe- includes primary somatic sensory cortex and sensory association area.

Primary motor cortex- only requires a small amount of stimulation to initiate movement. Premotor cortex- requires a higher stimulus to evoke movement. Dorsal and ventral areasregulates posture and movement so they are in optimum position. Dorsal area controls leg, trunk, arms, face (fine movement). Ventral area controls upper limbs- face, arms, some leg. Connection between the sensory and motor through practice and improvement through neurones developing. Somatosensory map and somatotopic (motor) map are close together, they are the same maps and the areas of the body are in the same places- so there are short pathways between the sense and the movement response. Size of the area that the map takes up is related to the sensitivity of the body part.

Supplementary motor cortex/area (SMA) is in the medial surface of the hemisphere (facing the middle). Split into 2 sections- SMA proper- contains somatotopic map, is connected to other motor areas and controls complex movement. preSMA- not well connected to other areas, but connected to the prefrontal cortex, plans complex movements based on previous experience.

Cingulate motor areasDorsal Ventral Rostral

Have somatotopic maps, and help with preparation of movement. Posterior parietal- collects sensory data from somatosensory cortex to help identify the target, assesses the contex and distance, puts it into 3D for voluntary movement.

Somatosensory map in- somatosensory cortex. Somatotopic map in- motor areas. Motor cortex links to the somatosensory and visual cortex. Cerebellum- makes up 1/10th of the volume of the brain. It contains ½ of all neurones in the brain. Involved in thought and higher brain function. Located at the back of the brain and connected to the brain stem by superior/middle/inferior cerebella peduncles. Receives information through somatosensory cortex through the brain stem. Links with thalamus and motor cortex. Connects with the vestibular system (eyes, ears, skin, muscle tendons). Damage causes a deficit in motor control, but not paralysis. Needed for voluntary movement, some reflexes and learning. Provides the timing signals to the cerebral cortex and the spinal cord for precise movement. Cerebral disease- ataxia- incoordination. Dysmetria- not smooth movement. Dysdiadochokinesianot being able to do rapid alternating movement. Tremor.

10/10/17 Basal ganglia. Has a striatum made up of the caudate nucleus, putamen and the globus pallidus (exterior and interior). Also has subthalamic nucleus Thalamus communicates with the basal ganglia but is not part of it.

The motor cortex sends signals to the basal ganglia, which links to the thalamus and then back to the motor cortex, to enhance or supress movement. The basal ganglia links to the cerebral cortex (motor), not somatosensory input or input from the spine. Controls movement through the direct and indirect pathway. The thalamus is a relay centre between the subcortical areas and the cerebral cortex. It receives input from every sensory system except the olfactory system. E.g- retina, thalamus, visual cortex. The direct and indirect pathway shows how the basal ganglia, thalamus and motor cortex link. Direct pathway: Activation of GABAergic neuron from corpus striatum to substantia nigra, GABA is released so inhibits the next GABAergic neurone from the substantia nigra to the thalamus, causing less inhibition of the Glutamatergic neurone from the thalamus to the motor cortex- so other positive neurone signals going to the thalamus will have an enhanced effect as it is not competing with as much GABA. The glutamatergic neurone is more likely to be activated, exciting the motor cortex and causing an increase in motor activity.

Indirect pathway: The GABAergic neurone between the corpus striatum and globus pallidus is activated, so GABA is released, this inhibits the GABAergic neurone between the globus pallidus and STN so less inhibition occurs and the glutamatergic neurone between the STN and substantia nigra is activated. Glutamate is released so that the GABAergic neurone between the substantia nigra and thalamus is activated. This causes an increase in GABA and inhibition in the thalamus, so it is harder for other neurones to stimulate it. The glutamatergic neurone between the thalamus and the motor cortex is inhibited so there is less glutamate and less activity. The indirect pathway involves more of the brain areas. STN and globus palidus is not involved in the direct pathway, only the indirect pathway.

12/10/17 Lateral and medial motor pathways.

Lateral- corticospinal and corticobubular tracts. Originate from a wide region in the cerebral cortex- including the primary motor, premotor, supplementary motor and cingulate motor areas. Corticospinal- terminates at all different levels, controls all the way down the body, can control interneurons to relax neurones, can activate motor neurones for contraction too. Can control fine movement (fingers). Corticobubular- terminates higher up (within neck at top of spinal cord) and controls the face and neck muscles.

Medial- most originate from the brain stem. Pontine and reticulospinal tract. Pontine- Important for gross movement and posture. Excitatory. Reticulospinal- inhibitory.

Brainstem involved in posture. Has 3 reflexes. Vestibular- eyes move to keep focus. Tonic neck- reflex in babies, so left leg goes down and right leg goes up so they can move from side to side. Righting- balance. Control pattern generators (CPG) give a rhythmic output for a regular movement e.g walking. Important for modification of movement.

Higher brain functions. Emotion and motivation. Shows the overlap between behavioural and cognitive systems. Key areas- hypothalamus, limbic system (amygdala, cingulate gyrus, hippocampus)- link between basic instinct and higher functions so it gives us more reasoning, cerebral cortex. Emotion- sensory stimuli comes into the cerebral cortex into the specific areas, information goes into the limbic system to create emotion, the signal goes back to the cerebral cortex so that it is aware of the emotion, hypothalamus and brain stem causes initiation of a response- somatic motor responses (voluntary and unconscious), autonomic response, can cause immune or endocrine response. Motivation- related to survival and emotions in higher thinking. Creates an increased state of arousal in the CNS, and goal orientated behaviour until satiety occurs (apart from OCD). Motivation can alter endocrine responses. Hunger causes you to eat, salt increases plasma osmolarity, the hypothalamus is activated, which stimulates the pituitary gland to reduce ADH to cause increased water retention in the kidney to reduce osmolarity. Pleasure and reward is linked to increased dopamine in the limbic system. Addictive drugs increase dopamine. Decreased dopamine in depression. Dopamine system originates from the VTA and releases it in the frontal area.

Learning- gaining knowledge. Associative learning and non-associative learning (habituationreduce stimulation, or sensitisation) Memory- retaining and recalling information. Stored in the cerebral cortex in memory traces. Sounds will be stored in auditory cortex, pictures stored in the visual cortex. Memory: short term (working), long term (reflexes- done so many times, or declarative- need to really think about it).

Short term- stimulus enters CNS, is limited and holds 7-12 pieces of information and then disappears. Working memory is processed in the pre-frontal lobes, collect facts from short and long term memory and integrate them for judgement of an action. Long term- consolidation converts short term to long term (time varies). Shows that the brain and neurones are plastic (can change and create new links to learn). Declarative memory can be transferred to reflexive (sports, reading, writing). Memory can differ based on perceptions and experiences. Language shows an advanced nervous system. Involves the left hemisphere of the cerebrum. Speech is the combination of sounds- vocalisation, and the combination of words. Wernicke’s area is close to the motor cortex so signals can be sent to it. Starts to process sensory info. Damage causes inability to understand writing or speaking. Broca’s area- outputs response. Damage causes inability to respond appropriately but they do understand. Input of language comes visually or audially. Reading- info into visual cortex, into Wernicke’s area, into Broca’s area and then the motor cortex. Listening- info into auditory cortex, into Wernicke’s area, into Broca’s area and then the motor cortex.

16/10/17 Sensory physiology.

Stimulus acts on a sensory receptor cell (may be neurone or epithelial cell that connects to a neurone). The receptor cell is a transducer which converts the external stimulus into an intracellular signal. Sensory receptors are diverse and specific. Can be simple or complex. Complex receptor organs have accessory structures. Sensory transduction- transduce physical and chemical signals to membrane potentials- receptor potential. Generates action potentials in sensory neurones. Sensory pathways- transmit to the CNS via specific pathways, for central integration and modulation of sensation.

Properties of sensory stimulus: Modality- information.

Location- direct or indirect (direction of sound). Intensity- proportional to the strength of the stimulus, translates as frequency of firing neurone. Duration- tonic receptors- slow adapting, activated as long as the stimulus is present. Phasic receptors- rapidly adapting, activated when stimulus first occurs but deactivates with constant stimulation.

Receptor neurones- specialised cells that respond to stimuli. Free nerve endings- bare dendrites, pain, temperature, tickle, itch and light touch. Encapsulated nerve endings (corpuscles)- dendrites enclosed in connective tissue capsule, pressure, vibration and deep touch.

Touch receptors respond to- pressure, stroking, texture, stretch, vibration. Receptors are in the skin as well as deep regions of the body. Nerve endings- hair root plexus. Encapsulated receptors- Merkel disc (steady pressure and texture), Meissner’s corpusles (stroking), Ruffini corpuscles (stretch), Pacinian corpuscles (vibration) are the largest receptor structures as they have a big accessory structure- layers of connective tissue, they respond best to high frequency vibration and are a tonic receptor.

Thermoreceptors- free nerve endings on skin surface. Cold receptors and warm receptors (based on body temperature). Adapt rapidly to changes at first but then has low frequency responses to keep us informed about ambient temperature. Pain signals produced 46 degrees.

Nociceptors (pain receptors)- free nerve endings at high density in the skin. Low density in bone, muscles, joints, viscera, blood vessels, meninges, peripheral nerve sheaths. Mechanical nociceptorsstrong pressure. Thermal nociceptors- extreme heat or cold. Chemonocireceptors- for harmful chemicals- capsaicin, potassium, extreme pH (lactic acid), histamine, bradykinin, prostaglandin (all inflammation). Polymodal nociceptors- combination. Capsaicin receptors for chilli heat only found in mammals. Sensory receptor adaptation- decrease in responsiveness for long lasting stimuli. Slowly adapting (tonic)- pain, body position. Rapidly adapting (phasic)- smell, pressure, touch, specialised for detecting changes. Receptive field of a sensory neurone is the region where the presence of a stimulus will alter the firing of the neurone. Different sensory neurones have different sizes of receptive fields. Touch receptors also have variable sizes. Receptive fields can overlap. Smaller receptive fields at higher density enhance discrimination between 2 stimuli.

Platypus- has electrical sense in bill- detect muscular contractions of their prey for hunting.

Snake- infrared heat receptors- in pit between eye and nostril. Processed in the same brain areas as visual information. Used for locating prey and predators and selecting warm spots.

Special senses are in special organs. In humans- chemical (taste, smell), ear (hearing, balance), photoreception (vision).

17/10/17 Special senses. Taste and smell. Purpose- detecting environmental chemicals, perceive danger (spoiled food, fire), for flavour, connection with thirst, hunger, emotion, sex, memory. Separate and distinct systems but merge at the cortex. Gustation requires a voluntary action, tastants must be soluble in water. Avoid bitterness, acidity, high salt content. Select foods with a high energy content- sugar, fat, alcohol. Taste buds sense sweet, sour, salty, bitter and umami. Taste experience- combination of tastes, smell, texture, temperature, pain. Ligands: Sour- H+ Salty- Na+ Umami- glutamate, nucleotides like MSG Sweet- sugars Bitter- cations-plant alkaloids Receptor cells in taste buds are epithelial or glial cells. Chemically sensitive on the apical side with microvilli that project into the taste pore of the taste bud. Tight junctions prevent anything else entering below the apical end, the tastant only interacts with the membrane protein on the outside. They are renewed every 2 weeks. Glial-like cells: most abundant, salt receptors, encloses the other cells with thin lamellae, do not form synapses. Receptor cells: have membrane receptors for sweet, bitter, or umami. Do not form synapses. Presynaptic cells: ion channel receptors for sour taste, have synapses with primary gustatory neurones. Have proton sensitive channels. Acids release H+ protons when dissolved in water. Receives paracrine input from glial-like and receptor cells. Serotonin is it’s transmitter substance with the neurone. The gustatory cortex compares information from multiple tastebuds. Taste signals don’t cross over to the opposite brain hemisphere. Taste sensations trigger and modify- salivation, gastric secretion, gastrointestinal motility.

Nutritional status determines food preferences. Aversion from food malaise. Satiety or repletion of nutrients makes a food more preferred. E.g protein deprived animals prefer umami taste. Breast milk is rich in umami and newborns are satisfied with a drop of MSG. Olfaction is not voluntary, odorants must have a high vapor pressure (tendency to evaporate from liquid to gas) so they can be inhaled. We can perceive over 100,000 odorants and distinguish between a few thousand of them. 20% are pleasant. Makes nutritious food pleasant. The nose warms or cools and moisturises the air we breathe. A small sample is passed to the olfactory epithelium deep inside the nasal cavity, containing olfactory receptors with cilia embedded in the mucus, the other side faces the olfactory bulb which protrudes from the cerebral cortex. It only covers 10cm 2. Receptors are continuously dividing. The odorant binds a membrane protein that activates a G protein which activates a biochemical cascade to release neurotransmitter. One signalling system, 1000 different odorant receptor proteins (3% of genome). The regions that interact with the G protein is highly conserved. The region that interacts with the odorant is hypervariable. The olfactory bulbs are one of the oldest parts of the brain and project to the olfactory cortex. It is part of the limbic system.

18/10/17 Hearing- perception of the energy carried by sound waves. Sound is generated by the vibrations of molecules in a medium. Vibrations represent changes in pressure during compression and decompression of molecules. Pitch- higher the frequency the higher the pitch (Hz), smaller wavelength. Normal hearing between 20-20,000Hz. Most sensitive at 1000-3000Hz. Loudness= amplitude (dB). Each 10 decibel increase represents a 10 fold increase in loudness. Normal conversation is 60dB. Above 80dB can cause receptor damage. Harmonic frequencies are secondary vibrations in relation to the fundamental frequency. Vary with the way the sound has been produced- why instruments have different sounds. Outer ear amplifies and directs the sound. Ear drum vibrates with the external sounds. Middle ear cavity filled with air contains 3 bones which amplify the movement of the eardrum onto the oval window. Inner ear (cochlea) is filled with endolymph fluid which vibrates with the movement of the oval window so the sound can be detected. Is divided lengthways by the cochlear duct, on either side are 2 compartments filled with perilymph. The cochlear duct rests upon the basilar membrane, where the organ of Corti is that contains auditory receptors. The auditory tube exposes the middle ear to atmospheric pressure by connecting it to the pharynx. It is normally closed but opens during sneezing, yawning and swallowing. Throat infections can block

the tube and cause fluid buildup in the middle ear. Bacteria trapped inside can cause ear infectionotitis media. Valsalva manoevre. Different parts of the basilar membrane resonate at different frequencies of sound. The adjacent section of the organ of Corti will vibrate with the basilar membrane. The receptors in the organ of Corti are the hair cells. They are mechanoreceptors with 50-100 hairlike stereocilia at one end which are covered by the tectorial membrane. When the stereocilia bend, ion channels open and the membrane is depolarised. Hair cells are non neural. They form synapses with primary auditory neurones using glutamate as a neurotransmitter. Axons from primary auditory neurones gather to form the cochlear nerve. The cochlear axons end in the brainstem where they form synapses with interneurons where processing and integration takes place. A multineuronal pathway transmits the informarion to the thalamus and further to the auditory cortex. Initial processing takes place in the cochlea for pitch, loudness, duration. Processing for localisation requires computation based on input from both ears and takes place in the brain. Hearing loss: conductive, sensorineural, central. Conductive- damage to the external or middle ear, ear canal plugged with wax or swollen due to infection/inf...