Exam

Function of neurons

Forms complex connections with other neurons

Performs computations inside the brain (thoughts)

Function of axons vs dendrites

Axons: transmit nerve impulses

Dendrites: receive nerve impulses from other neurons

Describe cell bodies

5-100 microns in diameter

dendrites are short (only few hundred microns)

Function of axon terminals

Secrete neurotransmitters in synapse.

3 types of neurons

1. Motor neurons: begin in CNS → exit via spinal cord → ends on muscle fibre

2. Sensory neurons: begin at sense organs (retina, skin, tongue) → convey info to brain via spinal cord

3. Interneurons: interposed btwn other neurons → does much of computation in brain

Describe Glial Cells

• 90% of cells in the brain, act as guidewires for growing neurons

• Provides supportive scaffolding for mature neurons later in development

• Assists in repair process when tissue is damaged

Describe the resting potential of a neuron

In resting state, inside of axon = negative by approx. -70 millivolts

• If a pulse is applied that exceeds excitation threshold (approx -55 millivolts), action potential occurs

• This causes inside to swing positive relative to the outside

How does resting potential work?

• depends on positive sodium ions (Na+) on outside of cell membrane

• Ion channels let charged ions in & out of the cell

• In resting state, Na+ ions are kept on the outside by sodium pump

• But in-going ion channels remain closed

What happens when a pulse is applied?

• In-going channels open → Na+ ions pour into cell → reverses voltage difference

• Na+ channels close → potassium (K+) ions go outside the cell

• Na+ pushed outside cell & K+ ions are drawn inside

• Inside & outside concentrations return to their original levels

Describe the Lock & Key Model

neurotransmitter molecules only affect postsynaptic membrane if molecule shape fits into certain synaptic receptors

Describe synaptic reuptake

• neurotransmitters don’t sit in the synapse

• inactivated by “clean-up” enzymes → reused in synaptic reuptake

Effect of drugs on the synapse

1. Stimulate or inhibit neurotransmitter release

2. stimulate or block postsynaptic receptor molecules

3. inhibit reuptake

Parts of the central nervous system (2)

Brain

Spinal cord

describe the parts of the peripheral nervous system

somatic nervous system: afferent, efferent, cranial nerves

autonomic nervous system: regulation of viscera (lungs, heart, blood, vessels, digestion, sex organs)

Function of afferent nerves (sensory)

transmit info from sense organs → brain & spinal cord

Function of efferent nerves (motor)

transmit info from CNA → effectors (muscle/glands that are the organs of action)

Function of cranial nerves

12 pairs - enter/exit from hindbrain (pons/medulla)

• poke through holes in skull (afferent/efferent functions)

• control movements of & carry sensations from head → neck

• regulate glandular secretions in head

• control visceral functions (automatic functions)

Describe Bell’s Palsy in relation to brain function

• paralyses part of the face → can’t form facial expressions

• e.g. smiling → one side may be fine while other side droops

• may never recover depending on severity

• may cause anixety & depression

• feel as if can’t go out due to physical difference compared to others

• may seek psychologist to come to terms with it

Describe the anatomy of a human brain

Two hemispheres → mirror images of each other

• left hemisphere: dominant for language

• right hemisphere: dominant for spatial awareness

Brain divided into 3 major parts: hindbrain. midbrain, forebrain (cortex)

Describe the parts of the hindbrain & their functions

Pons → arousal

• relays sensory info btwn cerebellum & cerebrum + other parts of brain

• regulates respiration

• involved in sleep & dreaming

Medulla

• regulates heart rate, blood pressure, respiration rate

• involved in vomiting, defecation, reflexes & swallowing

• in simpler animals: crawling/swimming motions

Cerebellum → knows what each body part is doing

• receives info from frontal lobes → knows what movements this lobe intends to accomplish

• monitors info abt posture/balance

• produces eye movements that compensate for changes in head position

• may play role in learning new movements & skills required

What happens when cerebellum is damaged?

1. Controls overall bodily balance

Damage (injury, disease, alcohol) results in wide stance & staggering gait

2. Sequencing & timing precise, skilled movements

Damage causes tremors during movement & inability to perform rapidly alternating movements

Describe the function of the midbrain

• Only basic functions for humans

• Auditory & visual stimuli → eye movement

• Control movements used in sexual behaviour & fighting → decrease sensitivity to pain

Midbrain difference btwn human brain & other species

Midbrain (animals - birds, floppy eared animals)

Very important

• Birds of prey → larger midbrains bc they’re involved in complex visual activity (e.g. scanning for prey)

• Fast, intricate activity (e.g. reaching ground quickly to catch prey)

Floppy eared animals

New sound heard → largely driven by midbrain activity

• Ears prick up & move towards sound to get more info via auditory canal

Describe the parts of the forebrain & their functions

Cerebral cortex

Outer shell of brain → crucial for psychological functions (allows more complex behaviours compared to animals)

• due to large cortex size in mammals, subcortical structures (e.g. midbrain) acts as relay stations for info

Gyrus (ridge on cerebral cortex)

• precentral gyrus → primary motor cortex

Involved in basic movement

• central sulcus → fissures

• postcentral gyrus → somatosensory gyrus

Involved in basic sensation

Describe the subcortical structures

Thalamus

Receiving & relay station for sensory input

• receives sensory info from sense organs → performs simple analyses → passes results to primary sensory cortex

Hypothalamus

Homeostasis (regulates important bodily functions) & species typical behaviours

• eating, drinking, body temp, sex

• controls most activity from Autonomic Nervous System (involuntary)

Basal Ganglia

Regulation & smoothing of movement → complex movements

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Describe one disorder associated with the basal ganglia

Huntington’s disease

Genetic disorder causing loss of control of voluntary muscles

• starts mild → severe

• difficulty eating: choking risk due to uncontrolled head & neck movements

Describe the different parts of the limbic system + functions (still forebrain)

Amgydala

Emotion recognition based on facial features (e.g. look of fear)

• aids survival by recognising facial expressions

• damaged → cannot feel/demonstrate fear when met with fearful stimulus

Hippocampus

Memory (formation, loss, etc.)

Effect of primary visual cortex damage

Causes scotoma (hole) in visual field like a blind spot

• black hole present in a specific area of visual field

• remove primary visual cortext → hemiaopia on opposite side

Effect of temporal/occipital lobe cortex damage

Prospagnosia

• difficulty recognising faces (familiar faces → can’t recognise a face as a face at all

Effect of prefrontal cortex damage

Phineas Gage → behavioural/personality change

• became violent

• lost ability to plan something & stick to it

Effect of right-sided parietal damage (neglect syndrome)

People with right-sided parietal damage tend to neglect left-side of space (permanent)

• no attention paid to auditory info on left

• believe left-sided limbs don’t belong to them (e.g. neglects using left arm)

• attention deficit - sensory/vision is unobscured

Accompanied by emotional component: anosognosia

• strong belief that there’s nothing wrong with oneself → hard to treat

• others addressing issue → aggravates person w neglect syndrome

Ways neglect syndrome patients exhibit implicit processing

Study - patients draw analogue clock

• numbers are all present, but crammed onto right side

• extends to other drawings copied

Define mechanical senses

things we sense

• physical touch (pressure on body, etc)

• hearing (vibrations)

Define chemical senses

Detecting which molecules are in air & food (whether they’re good or bad for us)

• Smell

• Taste

Define electromagnetic senses

Light = electromagnetic radiation bouncing off everything existing in world around us

• Sight

Describe transduction (mechanical system - touch)

Transduction: process of converting physical energy/stimuli into neural impulses in the nervous system

• converting energy or stimuli into a nerve signal for body to process → leads to conscious perception

E.g. touch

• skin = densely covered in mechanoreceptors

• neurone fires & sends signal to NS → travels to spinal cord → brain (somatosensory cortex)

Describe the auditory system (mechanical senses)

Sound waves differ in both frequency (pitch) & amplitude (loudness)

• auditory system channels & amplifies subtle vibrations in environment until it reaches cochlea

• transduction from vibration → nerve signals allows brain to make sense of sound

• vibrations activate basilar membrane (lining inside cochlear) via stereo cilia (tiny hair cells)

• frequency & amplitude affects how it vibrates

• e.g. loud sound = big vibrations

Describe olfactory system (chemical senses - smell + taste)

Olfactory receptor sounds have tiny holes in skull → passes through → binds to certain molecules

• specialised (lock & key mechanism) to only fire when they detect certain molecule

• air molecules get stuck in layer of mucus (cell dendrite rich)

• dendrites detect certain molecule → triggers action potential in cell body → sent to brain → smell transduced

Taste receptor cells in mouth (lock & key mechanism) transduce taste (similar to olfactory)

Describe vision (electromagnetic senses)

Pupil lets light pass through to the back (light = focused via the lens)

• how stretched out lens is can be changed via eye muscles

• changes where image is focused

Photoreceptors transduce light into nerve signals

• chemical inside photoreceptors undergoes chemical reaction when light hits it

• changes from one kind of protein into slightly diff shaped protein

• triggers cascade of chemical consequences → photoreceptors fire → sends action potential to other parts of eye & brain

Describe the anatomy of the retina

Retina: tightly packed w photoreceptors

1. Rods - in periphery; away from fovea (denser population) → responsive to wide set of wavelengths (S, M, L) → very sensitive

2. Cones (less in retina, 3 kinds that respond to diff wavelengths) → responds to colour

Centre = fovea

• looking at something (fixating) → image falls in the back centre of retina

How light leaves the retina

1. Light causes chemical reaction in rod and/or cone photoreceptors depending on its brightness & wavelength

2. Transduced into electrical signals in series of nerve cells in retina

3. Signals carried along axons (nerve fibres) in retina until they reach optic disc

4. At optic disc, all nerve fibres leave eyeball in bundle (optic nerve) → goes to LGN in thalamus to begin brain processing

How photoreceptors allow us to perceive colours

1. Photoreceptors gathered up by other kinds of cells through a few diff layers of processing within retina (centre-surround receptive field)
   receptive field = region of the visual field where light changes its activity
   centre = small circular region
   surround = ring-shaped region around centre
   centre (increases neuron’s firing rate) + surround (inhibits firing rate) are antagonistic

2. Info from cluster of photoreceptors gathered → collective signal sent to brain (allows efficiency for rest of visual processing)

3. Axons of retinal ganglion cells bundle up to form the optic nerve → via thalamus → eventually arrive at primary visual cortex

describe hierarchy of visual processing from the eye to the brain

For every little bit of visual field, there are thousands of edge-detecting (diff orientations) cells

• organised so that nearby neurones in V1 represent nearby bits of visual field

‘What’ pathway

• ventral stream (goes down temporal lobe) → neurones that respond to specific shapes, textures, parts of/whole objects → increasingly complex feature detectors as you go down pathway

‘Where’ pathway

• dorsal pathway (goes up brain) → neurones responding to specific speeds, directions, types of motion & reach areas involved in visually guided grasping

Describe challenges of visual perception

Visual perception = computationally hard bc recognising objects requires invariance to lots of complicated image differences

• difficult bc you must disregard all variation in actual image coming from external factors to recognise a 3D object in environment (e.g. lighting)

Position invariance

Although pattern is identical, diff positions mean image falls on diff parts of retina (completely diff photoreceptors → visual fields)

• brain must process position changes to recognise that it’s same image as before

how modern computer vision systems recognise objects

Systems coded to detect edges in images

• followed by machine learning - i.e. training it to recognise objects via trials

• deep neural networks made up of hundreds of layers of learning

biological vs artificial neurones

Biological neurone: strong synaptic connections where incoming neurone has strong effect on whether it fires (excitatory)

• OR weak ones (inhibitory)

• Hence incoming connection either increases/decreases probability of neurone firing

• Neurones recognise pattern (depolarisation threshold to fire action potential) → sends signal to other neurones

Artificial neurone

• each input has a weight

• big/small depending on how much influence you want the other neurone to have

• + or - depending on if you want it to increase/decrease existing activity lvl

• if there’s enough evidence to pass a threshold, continuous graded number is sent (instead of firing) to next unit

• Stacked continuously into complex web