Option A: Neurophysiology

A1, A2, A3, A4 6.5

nervous system process

sensor (eye, skin) → integration (brain, spinal cord) → effector (joints, muscles) in peripheral or central nervous system

Peripheral Nervous System

External nerves in muscles

• Autonomic- self regulated action of organs and glands

• Somatic- voluntary movements of skeletal muscles

Central Nervous System

Brain, spinal cord, links to other system

Neurons

• cells of the brain that transmit electrical impulses

• longest is in the whale

• ~86 billion in the body

dendrites vs axons

one is the projections from the cell that receive impulses from other neurones.

the other carries electrical impulses away from neurone to other neurones.

pre-synaptic terminal vs node of ranvier

place at the end of axon where electrical signal (action potential) is converted to a chemical signal (neurotransmitter).

allows ions to diffuse in and out of the neurone, sending signal jumping across gaps in the myelin sheath on the axon.

myelin sheath

myelination of nerve fibres allows for saltatory conduction

• axon is coated in schwann (type of glial) cells

• accelerates the saltatory conduction (travel) of electrical signals from node to node

• no myelin = slow transmission = multiple sclerosis

sensor neurones

receptor cell, myelin sheath, axon, cell body.

receive information from muscle receptors.

relay neurones

dendrite, cell body, pre-synaptic terminal, cell body

pass electrical signals across body.

motor neurones

dendrite, myelin sheath, cell body, node of ranvier, into muscle

send instructions to muscles.

visual cortex

• occipital lobe (hindbrain)

• controls the reception, segmentation and integration of visual information

• if damaged: loss of visual awareness, chronic blindness

Nucleus accumbens

• basal forebrain (one located in each hemisphere)

• controls wakefulness by expressing dopamine- pleasure, reward, addiction

• if damaged: less motivation, engagement, drive to achieve (similar results may occur after stopping antidepressants)

hypothalamus

• ventral brain (above pituitary)

• body temperature, hunger, thirst, mood, sex drive, blood pressure, sleep

• if damaged: dysfunctional homeostasis, body temperature, growth, weight, emotion, sleep, water control

pituitary gland

• base of brain behind nose bridge

• controls growth, metabolism, reproduction, secretes hormones into bloodstream

• if damaged: headaches, vision problems, nausea, fatigue, body composition change

medulla oblongata

• brain stem (connects brain and spinal cord)

• controls heart, circulation, breathing, blood pressure

• if damaged: respiratory failure, paralysis, loss of sensation

cerebellum

• back of head, above/behind spinal cord

• controls movement and balance, language, attention, eye movement

• if damaged: loss of coordination, distance blind, tremors, staggering, no rapid alteration between stimuli

Broca’s area

• posterior inferior frontal gyrus (front of brain)

• controls speech, articulation, comprehension, sensorimotor learning

• if damaged: breakdown between thoughts and language abilities

Ways to study the brain

Autopsy, dissection, removal of sections of animal brains, electrical stimulation of brains

Phineas Gage

Worker who had a tamping pole driven through his brain, resulting in the loss of his hippocampus. Subsequently more aggressive personality, loss of social inhibition.

Cerebral Cortex

• The outermost layer of the brain, has two hemispheres → responsible for higher order functions

• Human one is large with lots of folds- leads to high intelligence

• left side processes for right side of the body, right side processes for the left side

• corpus callosum connects the two hemispheres

Autonomic Nervous System

swallowing-

• voluntary phase gets food from mouth to pharynx,

• involuntary gets food from pharynx to stomach.

• controlled by cerebral cortex, medulla oblongata

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breathing-

• a) timing of inspiration,

• b) force of inspiration, voluntary expiration.

• controlled by medulla oblongata

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pupil reflex-

• controlled by medulla oblongata.

• muscles in the iris contract to dilate pupil and relax to constrict the pupil in response to light.

• If eye doesn’t immediately respond to light, may indicate brain death

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heart rate-

• controlled by medulla oblongata. monitors blood pH

• increases heart rate with the sympathetic system

• decreases it with the parasympathetic system

animal models for neuroscience and their applications

• drosophila- broad reaching, 4 chromosomes

• zebrafish- transparent tissues

• mus musculus- shares many human diseases

• xenopus laevis (African clawed frog)- large eggs

• caemorhabditis elegans (flatworm)- number of cells

used for ease of observation, simple systems and fewer ethical concerns.

embryogenesis

the process of making an embryo from a blastocyst.

• Requires gastrulation- the differentiation of tissue into the endoderm, mesoderm and ectoderm (three layers)

• after gastrulation, neurulation can occur to create an embryo.

neurulation (as observed in xenopus)

1. ectoderm tissue differentiates to form neural plate and neural plate border- notochord derived from mesoderm tissue

2. neural plate folds inwards and downwards, notochord pushed downwards

3. neural tube closes to form neural crest, which will differentiate into peripheral nervous system

4. mesoderm differentiates into somites (which will become bones and muscles), neural tube forms spinal cord, notochord degenerates into spinal disks

5. the whole tube becomes the brain at one end and the spinal cord at the other

spina bifida

condition caused by an incomplete closure of the neural tube during neurulation. Leads to:

1. myelomenyocele- sac of fluid forms in gap, part of spinal cord exposed in sac

2. meningocele- sac of fluid but spinal cord not exposed

3. spina bifida occulta- gap in spine, no sac

embryonic brain development

neural tube elongates to form forebrain, midbrain and hindbrain.

forebrain → (telencephalon → cerebrum) (diencephalon → thalamus)

midbrain → mesencephalon → brainstem

hindbrain → (melencephalon → pons + cerebellum) (myelencephalon → medulla oblongata)

development and migration of neurons

stem cells → progenitor cells → (neuron for signalling) (glial cell for support)

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• neural circuits- information networks connecting different types of neurons

• glial cells- scaffolding network that direct immature neurons to their destinations (only 1/3 of immature neurons make it)

• somal translocation- neuron forms an extension at the perimeter of its cell, and translocated its soma along this length

• axon growth is directed by chemoattractants and chemorepellents

synaptic density

neuroplasticity- ability for the neurons to change their pathways over time

• developing neurons form multiple synapses

• neural pruning removes unused neuron connections

• rerouting involves making new connections

• peak neural pruning occurs between 2-4 years of age, and highest neural density is at 2 years old

• sprouting allows the neurons to recover if one is damaged (eg if neuron A bonded to C is damaged, neuron B bonded to D will stretch to also bond to C)

  • for example, strokes may promote neural sprouting

parts of the eye

• lens- bends light to focus onto retina. flips/cones image, focus + clarity

• cornea- protects from UV radiation, focuses light entry

• eyelid- distributes tears, protects

• fovea- high acuity vision, focus, blind spot

• retina- light → images, photoreceptors

• optic nerve- one way connection from eye to brain, from retina

retina

1. light reflects off choroid, hits rods and cones

2. pigments in rods and cones break down, stimulating an action potential

3. synapses → photoreceptors → bipolar neurons → ganglia

4. ganglia carry impulse via optic nerve to occipital lobe in brain

rod cells

• many found around periphery

• dim light

• low resolution (many rods 1 cell)

• all wavelengths

• achromatic b&w

• one type- all contain rhodopsin

cone cells

• few found around centre

• bright light

• high resolution (1 cone 1 cell)

• red, green, blue only

• colour vision

• 3x different iodopsin pigments

visual processing

• optic chiasm- part of brain where optic nerves cross over

• optic nerve- connects eyes to brain

• visual field- portion of spaace in which objects are visible

• contralateral processing- each side of brain controls oppisite

• stereoscopic vision- register 3d visually

red green colour blindness

• sex linked on the x chromosome

  • mother needs to be at least a carrier, father needs to be colour blind for the child to be colour blind

• a problem with cones in the retina (responsible for colour recognition)

how is sound perceived in the human ear?

sound vibrations → chemical neurotransmitter

• eardrum is moved by sound waves

• eardrum causes movement of bones (incus, malleus) of the inner year- amplify sound by 20x on oval window

• causes movement of fluid in cochlear

• hair cells act as mechanoreceptors- sense movement, release a chemical neurotransmitter

• carried one way up auditory nerve to brain

structure of the ear

• eardrum vibrates movement

• bones vibrate against drum

• hair cells in cochlear generate neurotransmitter as sound passes over them

cochlear implant

• needed if auditory nerve is healthy, but hair cells are damaged or lost

sound → external mic → external supercomputer turns sound into digital information → sent to implanted device → sends electrical signal to electrode in cochlear → information goes up auditory nerve (bypasses hair cells)

vestibular system

controls balance

• located in the ear

• posterior canal- left right tilt recognition

• superior canal- up/down tilt

• horizontal canal- shake head “no”

head movement “sloshes” appropriate canal, movement detected by hair cells in cupula (wide base of each canal), transmitted into vestibular nerve so brain may deduce head movements, maintain balance

olfactory system

controls sense of smell

• receptor cells in epithelium of nose

• contain cilia (little hairs)

• membrane contains odorant receptor molecules

• only volatile substances (capable of readily changing state of matter) bind to receptor molecules

• different receptor proteins specific to different chemicals

innate behavior

inherited from parents, develops independently from environment

• reflexes

• kinesis

• taxis

• fixed action patterns

reflexes

involuntary, rapid response to stimulus detected by receptor

stimulus → receptor → sensory neuron → motor neuron (bypass brain) → effector muscle → response

= a reflex arc eg pain reflex to withdraw body part

kinesis

change in rate of activity in response to environmental stimulus

taxis

change in movement in response to an environmental stimulus → towards or away

fixed action patterns

pattern goes to completion even if stimulus is removed- involuntary

learned behaviour

based on experience and dependent on environment

non associative learning

habituation- getting used to a stimulus

sensitisation- more of a response to a repeated stimulus

associative learning- imprinting

• phase sensitive learning- occurs at a particular life stage

• independent of behavioural consequences- automatic

• filial (for parents) or sexual (partner)

associative learning- observation

watching and copying others’ behaviour after seeing results

associative learning- classical (reflex) conditioning

• unconditioned stimulus- leads to unconditioned automatic response

• unconditioned response- automatic to a stimulus eg salivation for food

• neutral stimulus- at first elicits no response

• conditioned stimulus- may eventually trigger a conditioned response

• conditioned response- must be learned by pairing a neutral stimulus with an unconditioned stimulus

learning to associate something with an action

Pavlov’s dog

paired the unconditioned stimulus/response of a dog salivating for food with the neutral stimulus of a bell. eventually the conditioned response of salivating when the bell is heard.

operant conditioning