Biology 1A - nervous systems and neurons Flashcards
what is neuroscience
study of the nervous system; including cellular and molecular processes, behavioural, affective and cognitive abilities, systems or circuitry, and disease.
what is a neural unit
brain is made up from individual neurons that contain specialised features (dendrites, cell body, axon)
what is neuron specialisation
units may differ in size, shape, structure according to location or functional specialisation
what are neuronal fibres
outgrowths of neurons
what are neuronal contacts
neurons are connected by sites of contact and not cytoplasmic continuity
what is dales law
each neuron had a specialised chemical (eg. neurotransmitter)
what does a neuron consist of
- Dendrites (transmits information from sensory receptors, other neurons)
- Cell bodies (integrate information; also have a nucleus)
- Axon (signal output, passes information to subsequent neuron)
what are the types of neuroglia ( hold nerve cells in place)
ependymal cells
astrocytes
microglia
satellite cells
Schwann cells
oligodendrocytes
describe the 6 layers in the human neocortex
input = primality to layer 4 stellate cells
output =primarily layer 5 and 6, pyramidal cells
integration = (of information), remaining layers
layers may be sub-divided
what are the different action potential activities that sensory neurons can exhibit depending on stimulus?
phase response (one big spike)
tonic response (multiple big spikes)
what do chemical channels in neurons do
help maintain a resting potential and the voltage gradient
describe chemical channels in neurons/axons
- sodium and potassium ion channels are abundant in neurons/axons
- potassium feely moves through channels (1:1 ratio)
- sodium is tightly regulated
- the sodium- potassium exchange pump costing 1 ATP
- chloride (-) and calcium (+) are also important for maintenance of electrochemical gradient
what do the nodes of Ranvier do
increase speed at which voltage is transmitted down axons
what is multiple sclerosis
an autoimmune disease associated with the loss of myelin; disrupts the transfer of nerve signals causing a wide range of symptoms such as
- loss of vision
- ataxia
- fatigue
what is myelin sheath composed of?
layered glial cell membrane
describe chemical communication across the synapse
action potentials reaching the synapse stimulate chemical communication; ions and other molecules
1) terminal is at rest
2) AP arrives, vesicles fuse with terminal membrane producing exocytosis of transmitter
3) transmitter binds to postsynaptic receptor proteins, ion channels open
4) transmitter is removed from the cleft; fused membrane is recycled
what stimulates the release of transmitter from intracellular vesicles in presynaptic neuron?
voltage gated calcium channels
describe ionotropic (fast) receptor signalling and post synaptic neuron.
- ligand gated ion channel
1) neurotransmitter binds directly to the channel protein
2) channel opens immediately
3) ions flow across membrane for a brief time
describe metabolic (slow) receptor signalling in the post synaptic neuron
- G protein- coupled receptor
1) neurotransmitter binds to G protein- coupled receptor
2) G protein is activated
3) in this case, activated g protein subunit moves to adjacent ion channel, which causes brief delay
4) channel opens and ions flow across membrane for a longer period of time
what does the hypothalamus control?
- endocrine regulation
- autonomic function
- limbic function
what part of the brain is the hypothalamus part of
diencephalon
what is the neuron doctrine
the concept that the nervous system is made up of discrete individual cells
what are the different sections of the human brain
1) cortex and deep structures of cerebellum
2) thalamus and hypothalamus
3) brainstem = mesencephalon, midbrain pons and medulla
4) cerebellum
what are the key principles of brain organisation
1) most sophisticated functions: conscious awareness, decision making etc. are located at the top and front of our brains
2) older more primitive systems are not removed through evolution
3) localisation of function is straight forward for older systems, but not so for higher order systems eg. long term memory
what protects the brain
skull
meninges
cerebral spinal fluid (CSF)
what is cerebral spinal fluid (CFS)
solution that provides an environment that insulates the brain
what is the blood brain barrier
barrier around brain that ensures only essential molecules (eg. glucose/ oxygen) pass into the brain
what is a ventricle in the brain
hollow space in the centre of the brain filled with fluid
what three things can happen at a synapse
excitation
inhibition
modulation
how does the brain create sophisticated mental function
nature (genetic, evolution)/ nurture (experience, environment)
what are the divisions of the central nervous system
1) afferent division
- sensory stimuli
- visceral stimuli
2) efferent division
I. somatic nervous system => motor neurons => skeletal muscles (effector organ)
II. autonomic nervous system => parasympathetic ns and sympathetic ns => smooth muscle, cardiac muscle, some endocrine glands (effector organs)
II. autonomic nervous system and stimuli in digestive tract => enteric nervous system => digestive organs only
what does the autonomic nervous system do?
- contains sympathetic and parasympathetic (target same tissues and have opposite effects)
- controls basic physiological functions eg. thermo regulation, digestions, circulation etc
- work to maintain homeostasis
what are the nerve connections of the autonomic pathways
1) preganglionic fibre (between CNS and autonomic ganglion):
- sympathetic reside in spinal chord (thoracic and lumbar)
- parasympathetic originate in brain and lower spinal chord
(both secrete acetylcholine)
2) postganglionic fibre (between autonomic ganglion and effector organ):
- sympathetic secrete norepinephrine and are adrenergic fibres;
- parasympathetic secrete acetylcholine and are cholinergic fibres
what is the adrenal gland (autonomic nervous system) and what are its two different structures?
endocrine tissue involved in stress
1) adrenal medulla - “postganglionic like”: secretes epinephrine and norepinephrine
2) adrenal cortex - secretes mineralcorticoids and glucocorticoids
how is blood supplied to the brain
2 pairs of arteries
1) internal carotid arteries (anterior 2/3 of the brain)
2) vertebral arteries (posterior 1/3 of the brain)
circle of Willis (blood supply to brain)
branches from both internal carotid arteries and vertebral arteries that form an important anastomosis on the inferior surface of the brain (in subarachnoid space)
it allows blood entering the brain via ICA and vertebral arteries to be distributed to any part of both hemispheres
what arteries are part of the circle of Willis
- anterior, middle, and posterior cerebral arteries
- anterior and posterior communicating arteries complete the circle
what is a stroke
interruption of blood flow to the brain causing cell death
what are the risk factors for strokes
- sex, age, ethnicity, family history
- hypertension, heart disease, high blood cholesterol, diabetes, smocking, obesity
what are the two types of stroke
1) ischemic - blockage of a vessel supplying the brain (85%)
2) when blood vessel supplying brain leaks or ruptures (15%)
what is an intercerebral and subarachnoid bleed
intercerebral = bleed within brain
subarachnoid = bleed on surface of the brain
could be caused by haemorrhagic stroke
what can be the result of a stroke
- inability to move one or more limbs on one side of body
- inability to understand or formulate speech
- inability to see one side of visual field
how can strokes be diagnosed
scans = PET, MRI, CT, Angiogram, Perfusion imaging
what are the symptoms of a stroke
- severe headache
- loss of motor skills
- weakness, numbness of face and limbs
- difficulty with speech and swallowing
- seizures
- confusion
how do endocrine systems communicate with the CNS (chemical signalling)
bi-directional communication
feedback system:
endocrine system influences sensory and motor systems which lead to behavioural effects which then influence other systems
describe neuroendocrine communication (neuroendocrine systems)
1)presynaptic neuron, propagation of action potential and release of neurotransmitter into synaptic cleft
2) neurotransmitter acts on receptor on post synaptic neuroendocrine cell
3) neuroendocrine cell is activated by binding of neurotransmitter to receptor and releases a hormone into circulation
4) hormone travels in circulation to target tissue
what are neuroendocrine cells closely related to
blood vessels so can release hormones into circulation
describe endocrine cells (endocrine signalling)
- no involvement with nervous system to synthesise and release hormones
- found in any tissue
- will respond to a signalling molecule (eg. hormone released from neuroendocrine system) binding to specific receptor leading to release of hormone by endocrine cell
- in highly vascularised tissue
- specialised for synthesis, storage and release
what must a target cell posses (endocrine signalling)
specific receptor for that type of hormone allowing it to respond
receptor can be located on the cell membrane or in the cytoplasm
what are the endocrine glands in the body?
CNS:
- hypothalamus
- pituitary gland (influenced by hypothalamus)
- pineal gland (release of melatonin)
Body:
- thyroid gland (growth hormone and metabolism)
- pancreas (glucagon and insulin)
- adrenal gland (on top of kidneys)
- gonads
describe the hypothalamus (neuroendocrine system)
- controls homeostasis and many body systems (e.g. sexual behaviour, energy balance)
- has different areas/ nuclei, each with a distinct function
- most nuclei communicate with endocrine system via pituitary gland
what does nucleus mean in terms of the central nervous systems (neuroendocrine systems)
a specific region with a specific function
what are the two parts of the pituitary gland (neuroendocrine systems)
- anterior pituitary (releases hormones)
- posterior pituitary
what is the hypothalamic-anterior pituitary axis (neuroendocrine systems)
relationship of the hypothalamus and the anterior pituitary gland
describe the hypothalamic- anterior pituitary axis (neuroendocrine systems)
- neuroendocrine cells project from hypothalamic nuclei into the median eminence
- they release neuropeptide hormones into hypophyseal circulation (blood vessel in median eminence)
- blood drains via hypophyseal veins into anterior pituitary
- stimulates (or inhibits) release of hormones from anterior pituitary into circulatory system
what is the hypothalamic-posterior pituitary axis (neuroendocrine systems)
relationship between the hypothalamus and posterior pituitary gland
describe the hypothalamic- posterior pituitary axis (neuroendocrine systems)
- neuroendocrine cells from the paraventricular and supraoptic nuclei project to the posterior pituitary
- neuropeptide hormones released directly into circulatory system within posterior pituitary
- only 2 neuropeptides released from posterior pituitary:
vasopressin (ADH) (paraventricular nuclei)
oxytocin (supraoptic nuclei) - posterior pituitary doesn’t directly synthesise and release own hormones, hypothalamus projects to posterior pituitary and releases its own hormones there
what are the functions of the two hormones released from the posterior pituitary gland (neuroendocrine systems)
- vasopressin (ADH) (controls water balance and blood pressure)
- oxytocin (lactation, uterine contraction)
what hormones are released from the anterior pituitary? (neuroendocrine systems)
- FSH ( acts on ovaries to induce release of oestrogen and progesterone)
- LH (acts on testes to induce release of testosterone)
- growth hormone (GH) - growth of long bones
- THS (thyroid stimulation hormone) - acts on thyroid gland to induce release of T4 and T3
describe male neuroendocrine-gonad feedback
1) hypothalamus releases gonadotropin releasing hormone (GNRH)
2) acts on anterior pituitary to stimulate release of FSH and LH
3) FSH acts apon testes Sertoli cells leading to sperm production
4) LH acts apon testes Leydig cells leading to testosterone production
5) testosterone acts apon target cells and also feeds back to pituitary and hypothalamus inhibiting further release of GNRH, FSH and LH (negative feedback)
describe female neuroendocrine-gonad feedback
1) release of gonadotropin releasing hormone (GNRH) from hypothalamus
2) triggers release of LH and FSH from anterior pituitary
3) FSH acts on ovaries and stimulates maturation of the follicle, releasing oestrogen
4) LH triggers development of corpus luteum and release of progesterone
5) oestrogen released by follicle => negative feedback on anterior pituitary and hypothalamus => halfway through cycle switches to positive feedback => stimulates increased release of LH => release of progesterone
6) increased progesterone in second half of cycle => negative feedback on hypothalamus and anterior pituitary
describe Leydig cells and Sertoli cells within the testes (neuroendocrine systems)
Leydig cells: found between seminiferous tubules, produce testosterone in response to LH binding to receptors on cell membrane
Sertoli cells: within seminiferous tubules, respond to FSH which stimulates sperm maturation
describe hormone release in the ovary (neuroendocrine systems)
- FSH stimulates follicle maturation
- mature follicle has layers which secrete hormones
- theca cells in follicle produce androstenedione hormone
- granulosa cells in follicle produce oestrogen
- one oestrogen released negative feedback => halfway switch to positive to increase progesterone
describe the neuroendocrine- thyroid axis
1) hypothalamus releases thyro-tropin releasing hormone
2) acts on anterior pituitary to release TSH
3) stimulates release of T3 and T4 from thyroid gland
4) T3 and T4 has negative feedback effects on the hypothalamus and anterior pituitary
describe the neuroendocrine-adrenal axis (stress response)
1) hypothalamus neuroendocrine cells release corticotropic releasing hormone (CRH)
2) stimulates release of ACTH from anterior pituitary
3) travels in circulation until acts of adrenal cortex which stimulates release of hormones
describe the parts of the adrenal gland (neuroendocrine-adrenal axis)
adrenal medulla = under influence of sympathetic nervous system, produces epinephrine/norepinephrine (adrenaline)
receives sympathetic innervation from the spinal chord
adrenal cortex = responds to ACTH released from corticotrope cells of posterior pituitary, zonas of cortex produce hormones associated with stress response (cortisol and aldosterone)
describe the pineal gland (neuroendocrine systems)
source of melatonin
contain Pinealocytes that produce melatonin which is a hormone involved in the sleep/ wake cycle
what are Pinealocytes derived from (pineal gland)
photoreceptors
describe patterns in melatonin (neuroendocrine systems)
1) low melatonin levels in CSF during the day
2) high melatonin spikes at night
3) winter - longer duration of melatonin spike
what does oxytocin do? (neuroendocrine systems)
induces myoepithelial cells to contract leading to milk let-down
describe the process of milk release from a mother (neuroendocrine systems)
1) infant sucking response produces brain activity in the mother
2) increased brain activity results in inputs to the hypothalamus
3) oxytocin produced and released from posterior pituitary
4) causes cells of mammary glands to contract; releasing milk
what does cholesterol synthesise (specificity of hormones)
steroid hormones
what determines which hormones are synthesised from cholesterol (specificity of hormone actions)
specific enzymes produced by endocrine cells
if aromatase enzyme is present what does this indicate (specificity of hormone actions)
that oestrogen is present and having an effect
describe the stress response
1) stress detected
2) hypothalamus releases corticotrophin-releasing hormone
3) acts on pituitary gland to release adrenocorticotropic hormone
4) acts on the adrenal cortex to produce glucocorticoids and the adrenal medulla to produce epinephrine and norepinephrine
what can be observed on days of high stress eg. exam day (stress response)
a spike in epinephrine and norepinephrine
what can be an effect of long term stress (stress response)
can have detrimental impacts for example can inhibit healing of wounds
what are circadian rhythms (biological rhythms)
they are daily biological cycles
roughly 24hr cycles in the body
controls things like alertness, temperature, hormones etc.
how are circadian rhythms regulated (biological rhythms)
environmental cues (exogeneous zeitgebers)
eg light exposure for sleep wake cycle
what hormone is released when the body feels stress (biological rhythms)
cortisol
what is the suprachiasmatic nucleus (SCN) (biological rhythms)
- specialised group of hypothalamic cells
- brains master circadian pacemaker
- controls sleep wake cycle
how does the SCN control sleep wake cycle (biological rhythms)
- receives info from about light exposure from ganglion cells in retina along the retinohypothalamic tract
- this activates melatonin secretion by pineal gland
describe an early study into the SCN and circadian rhythm’s ( biological rhythms)
SCN of rat with 20 hour period was transplanted into rat with 27 hour period => recipient adopted 20 hour period indicating that SCN controls sleep wake cycle
describe actions of melatonin throughout the sleep/ wake cycle (biological rythms)
- melatonin is sleep promoting hormone released by pineal gland at night
- suppressed by light exposure
- production increases in evening, peaks in middle of the night, fall to daytime low in morning
how can circadian rhythms be measured (biological rhythms)
- dim light melatonin onset = time ay which melatonin levels rise above threshold under dim light conditions in lab
- measured via saliva or blood sample
- reliable marker of individuals circadian phase
what can cause circadian rhythm disorders (biological rhythms)
jet lag
shift work
what is an example of societal pressure affecting circadian rhythms (biological rhythms)
early school start times
cuts sleep short resulting in insufficient sleep on weekdays
creates permanent state of social jet lag
what are the consequences of short/ ill timed sleep (biological rhythms)
- cognition and academic performance
- safety (road collisions)
- mental health (depression/ anxiety)
- physical health (obesity)
how does sleep deprivation affect emotional wellbeing (biological rhythms)
- weekday sleep selectively deprives of REM-rich final hours
- REM important for emotional regulation
