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Neurons, SENSATIONS AND VISION, NERVOUS SYSTEM, PERCEPTION AND VISUAL…
Neurons
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COMPONENTS OF A NEURON
- Dendrite (tree)
- receiving portion of neuron
- many branches to increase neuron's SA
- Soma (cell body)
- makes proteins and building blocks of neurotransmitters (CMs)
- contains DNA
- vital to cell function
- Axon
- sending portion of the neuron
- long thin fibre
- axon terminal: end of axon which contains synaptic vesicles with neurotransmitters
- myelin sheath: white, fatty substance that insulate signals
4.synapse:
- gaps between neurons
- information is exchanged here
GLIAL CELLS
overview
-glia: support cells (glue) of the NS, 10x more numerous than neurons
1.Oligodendrocytes:
- form myelin sheath covering of axons in brain and spine
- called Schwann Cells in the rest of the body
2.Astrocytes:
- provide nutrients to neurons
- help communication between neurons
- provide connections between neurons and blood vessels
3.microglia:
- remove debris, waste, damaged cells from nervous system via phagocytosis
TYPES OF NEURONS
- Sensory Neurons:
- receptors
- receive input from the sensory organs (eyes, ears, nose, mouth, skin) and send it to the brain
- Motor Neurons:
- effectors
- send output from brain to muscle and organs
- enables the body to move
- sometimes signal does not go through brain because it is too slow
- Interneurons
- processors
- thousands of times more numerous than sensory and motor neurons, and relay information between neurons in the brain
NEURON COMMUNICATION
overview:
- communicate by chemical and electrical activity
ELECTRICAL COMMUNICATION
neurons at rest:
- have three different types of ions passing in and out of them at different rates
- chloride, potassium, sodium
- are polarized
- electrical charge inside is negative and outside is positive
neurons at wake:
- incoming messages from other neurons can generate a neural impulse called an action potential
- sodium ions rush in and out along the axon, propagating the electrical signal
- electrical state is called depolarized
- message must be strong enough (reach activation threshold) to generate the impulse
- once impulse is generated, all-or-none law
neurons after firing:
- cannot fire again for a brief period
- called the absolute refractory period
- electrical state is hyperpolarized
- electrical charge inside is even more negative than at rest
- due to chloride ion influx and potassium and sodium ion efflux
- neurons go back to resting potential
CHEMICAL COMMUNICATION
overview:
- neurons communicate with other neurons via chemical messengers called neurotransmitters
- after an action potential, neurotransmitters are released from the axon terminal into the synapse and are received by the dendrites of the next neuron
8 steps of synaptic transmission:
- synthesis: neurotransmitters are made in the soma
- transportation and storage: neurotransmitters are taken to axon terminal for storage
- release: action potential causes release of neurotransmitters into synapse
- binding: neurotransmitters bind at receptor sites on dendrites of next neuron
- deactivation: neurotransmitters are destroyed in the synapse
- autoreceptor activation: some neurotransmitters bind back to receptor sites on the original neuron
- reuptake: leftover or excess neurotransmitters are brought back
- degradation: too much leftover or excess neurotransmitters are broken down
OVERVIEW
- human break contains 86 billion neurons, and a 100 trillion connections between them
- separated from each other by synapses
Hebbian Learning Rule
- Donald Hebb: single neurons don't influence behaviour; entire complex networks of them called assemblies do
- hebbian learning rule: neurons that continually fire together, wire together -> basis of learning
- long term potentiation: persistent strengthening of synapses based on recent patterns of activity
SENSATIONS AND VISION
OVERVIEW
Sensation:
- detection and sensory experience of stimuli in our environment, including sounds, smells, tastes, and images
perception:
- the meaningful integration, organization, and interpretation of sensory information
- processes and overlaps with sensation and vice versa
psychophysics:
- study of how physical stimuli are translated into psychological experience
synesthesia
- mixing of senses
- e.g., hearing colours
SENSATION
overview:
- occurs because sensory receptors, stimulated by physical energy in our environment, transmit neural impulses to our brain
Sensory Thresholds:
- we do not have infinite capacity to detect all levels of energy
- for sensation to occur, stimulus must be strong enough to be detective (e.g., loud enough to be heard)
- i.e., stimulus has to be strong enough to reach the sensory receptors' activation threshold
Sensory Adaptation:
- humans do not detect same stimuli with the same intensity over time
- in fact, sensory receptors become less responsive to a constant stimulus
- this decreases sensitivity to a constant stimulus over time is called sensory adaptation
- become acclimatized
subliminal perception:
- perception without awareness
- often used in advertising
VISUAL SYSTEM: SIGHT
light allows for sight
- sense organ for vision is the eye, which contains sensory receptors that are sensitive to a physical energy called light
- different types of EM energy have different wavelengths, each containing a different colour (in the visual spectrum
three dimensions of our perception of colour:
1.hue: colour or shade of stimulus determined by wavelength of light
- short wavelength = high frequency = bluish colours, high-pitched sounds
- long wavelength = low frequency = reddish colours, low-pitched sounds
- brightness: intensity of electromagnetic radiation (determined by amplitude)
- large amplitude = bright colours/loud sounds
- small amplitude = dull colour/soft sounds
- as brightness increases, results in white, decreases, results in black
- saturation: relative purity of light being perceived
- faded vs. concentrated
EYE
muscles:
- suspended in the orbits, bony pockets in front of the skull
- held in place by 6 extraocular muscles (allows us to move our eyes in different direction)
movements:
- vergence: cooperative movements that keep both eyes fixated on a target
- converging on a target
- further away, less turned in (verged) eyes have to be
- saccades:
- jerky movements to shift gaze (stop between them = fixations)
- smooth pursuit: slow, stimulus tracking movements
issues
issues with vergence:
- strabismus: eyes do not properly align with each other when looking at a stimulus
- four types
- esotropia: eyes are crossed (cross-eyed)
- exotropia: eyes are diverged (lazy-eyed)
- hypertropia: eyes are vertically misaligned, pointing upwards
- hypotropia: eyes are vertically misaligned, pointing downward
EYE MECHANICS
eye muscle movements
accomodations:
- the thinning and thickening of the lens to focus light on the retina
- via contraction of the ciliary muscles
- if the eyeball is abnormally shaped, the length has trouble focusing light on the retina
- results in visual disorders
visual disorders
myopia
- also called nearsightedness
- when far objects appear blurry because light reflected off objects focuses in front of the retina
hyperopia:
- farsightedness
- when near objects appear blurry because light reflected off objected focuses behind the retina
presbyopia:
- farsightedness
- arises in middle-age because the lens becomes brittle and less flexible
astigmatism:
- when lens or cornea are abnormally curved, leading to blurry vision because light is focused in multiple points on the retina
eye parts
cornea: a clear membrane that covers the front of the eyes, and helps gather and direct incoming light
pupil: a black opening in the center of the eyes
lens: a clear membrane that thins or thickens to bend of focus incoming light to ensure that if falls on the back of the eye (retina)
Iris:
- surrounds pupil; the coloured part of the eye
- ring of muscular tissue that contracts and expands to control the size of the pupil in response to light
- the more light, the more the iris will expand to decrease pupil diameter
RETINA:
- a thin, light-sensitive membrane that lines the back of the eye
- contains photoreceptors (light receptors) called rods and cones
photoreceptors:
- rods: (120 million) are more numerous than cones (6 million) and are better adapted for seeing in dark conditions
- cones: adapted for seeing in bright conditions, including seeing colour and fine detail
- highest concentration of cones is in the fovea centre of the retina; there are no rods in the fovea
- exists in the centre of the visual field
- highest visual acuity
optic disk:
- area of the retina that lacks photoreceptors, where the optic nerve exits the eye called the optic disk
- thus, we have a tiny blind spot in our field of vision
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NERVOUS SYSTEM
BRAIN
Protection
overview
- CNS protected by bone casing
- Brain protected by skull or cranium
- spinal cord is protected by vertebral column
meninges
- beneath the skull
- from ancient greek "membrane"
- there are 3 membranes that envelope the brain and spinal cord (CNS)
- Dura Mater: outer; hard, thickish, acts as shock absorber
- arachnoid mater: middle; "spider", looks like spider web membrane
- pia mater: gentle membrane, hugs surface of brain
- cerebrospinal fluid (CSF: located between the arachnoid mater and pia mater
- to protect the CNS
Parts of brain
1. Forebrain
overview:
- contains cerebrum, divided into 4 lobes, basal ganglia, basal forebrain, thalamus, limbic system
Cerebrum:
- largest part of the brain
- controls voluntary actions, senses, and cognitive function
- surface is called cerebral cortex (made up of gray matter - neuron cell bodies), and is folded up so that it can fit inside the skull
- hills or bumps are called gyri (singular = gyrus)
- valleys or grooves are called sulci (singular = sulcus)
- divided into two halves, called left and right hemispheres
- right hemisphere controls voluntary limb movements on the left side of the body, and left hemisphere controls voluntary limb movements on the right side of the body
- called contralateral control
- a broad band of nerve fibres called the corpus callosum links the two cerebral hemispheres
- nerve fibers are white matter (axons of the neurons that are coated in myelin
cerebral lobes:
- each hemisphere divided into 4 lobes
- frontal lobe:
- includes:
- primary motor cortex: voluntary body movements
- broca's area: language production
- executive factors: thinking, planning, decisions
- contain mirror neurons: activate when you see other people performing actions
- parietal lobe:
- primary somatosensory cortex: sensations of pressure, pain, and temperature
- space and object orientation
- occipital lobes:
- back of brain; responsible for vision
- temporal lobe:
- hearing, complex facial tasks
- Wernicke's Area: language comprehension (comprehending others and making your own language comprehensive
DAMAGES TO BRAIN
frontal lobe damage:
- difficulty reasoning, making decisions
- inability to control emotions
- goal directed behaviour impairments
Broca's Area: Expressive/Broca's Aphasia
- difficulty producing speech
occipital lobe damage:
- blindness/visual hallucinations
temporal lobe damage:
- Wernicke's Area: Wernicke's Aphasia; difficulty comprehending language and making language comprehensible
forebrain also includes:
- Basal Ganglia: control of voluntary movements (with help of motor cortex)
- routine behaviours or "habits" such as teeth grinding, eye movements, emotion
- cluster of grey matter than helps out a lot with frontal lobe functions
- basal forebrain: activates cerebral cortex, attention
- thalamus: sensory gateway to the cerebral cortex; functions as a relay station for all sensory impulses to the cerebral cortex (excluding smell)
Limbic System: emotional centre
- networked with the autonomic NS to influence blood pressure, heart, and endocrine system
- conveys information about our internal state
- hypothalamus:
- maintains the body's internal states (homeostasis) by overseeing the endocrine and autonomic NS
- amygdala:
- plays a key role in processing of emotions, especially fear and pleasure
- plays a role in memory
- Cingulate Cortex: involved in emotional expression
- knowledge of socially appropriate behaviour
- regulates ANS
- Hippocampus:
- spatial memory, fear conditioning
- only place neurogenesis can occur besides in the olfactory orb
2. Midbrain:
overview:
- integrates sensory processes, such as vision and hearing
- contain important network of dopaminergic neurons
Reticular Formation:
- modulates muscle reflexes, breathing, pain perception, sleep, and arousal
3. Hindbrain:
overview:
- contains two important structures
brainstem:
- oldest part of the brain, beginning where the spinal cord swells and enters the skull
- responsible for automatic survival functions
- includes three structures:
- medulla oblongata: crucial for life; controls breathing, swallowing, blood pressure, and heart rate
- pons: bridge; links cerebrum to cerebellum, and relays signals between them
- also plays a key role in sleep and dreaming
- midbrain: controls rudimentary vision and hearing
- basic, low level, sensory integration
Cerebellum:
- means "little brain" in Latin
- responsible for balance and coordination of muscles
- important for voluntary tasks (e.g., walking, reaching, writing)
Brain asymmetry:
- lateral organization of function
- some functions controlled by one side more than others
- language more associated with the left brain
- spatial ability/mathematical skills more right brain
- left handed people can have this switched
- women outperform males at language processing tasks (vocabulary especially)
- men have upper hand in mental rotation of 3D images
2 DIVISIONS OF THE PNS
Somatic Nervous System:
- control voluntary behaviour
- contains sensory and motor neurons
- sends sensory information to the CNS, and carries info from the CNS along motor neurons for voluntary movement
Autonomic Nervous System:
- controls involuntary functions
e.g., heartbeat, breathing, digestion
- activates fight or flight responses
- components
- sympathetic nervous system:
- body's emergency system (activates body in response to threat or emergencies
- parasympathetic nervous system:
- body's conservation system (conserves and maintains body's resources; calms you down after an emergency)
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