block 2- the nervous system Flashcards
describe the gross anatomy of the brain and spinal cord
CNS
brain:
cerebrum = largest part, each hemisphere controls opposite side of body
cerebellum = “little brain”, co-ordinates movement
brain stem = controls vital functions composed of pons, midbrain and medulla
spinal cord = communication link between brain and body
gyri = ridges
sulcus = grooves that seperate lobes
pons = round bit of brain stem
medualla = elongated bit
anatomical references for the CNS components
rostral = front of body (head)
caudal = back of body (tail)
dorsal = back/top (posterior)
ventral= front eg stomach in spinal cord (anterior)
mid saggital section = sliced dirrectly in middle
para saggital section = off center
what does lissencephalic and gyrencephalic mean and what kind of species display each kind
- lissencephalic = brain appers smooth
- rats, rabbits - gyrencephalic = brain appears grooved
- humans, primates, dolphins
describe the central, lateral, pareito-occipital and calcarine sulcus’ of the brain
- central sulcus
- separates the frontal and parietal lobes, between the pre and post central gyrus
- shows location of primary motor cortex and primary somatosensory cortex - lateral sulcus
- separates the frontal and pariental lobes from the temporal lobe
- also known as Sylvian Fissure - Parieto-occipital sulcus
- between the pariental and occipital lobes - Calcarine sulcus
- within occipital lobe
- shoes location of primary visual cortex
what is the internal capsule?
= a white matter structure in the brain that connects the cerebral cortex to the spinal cord and brainstem
- any neuron travelling through the brain must pass through it
what are the three lobes of the cerebellum and what gives it it’s large surface area?
lobes:
- anterior
- posterior
- flocculonodular lobe
- large surface area due to the folia
describe the three compoennts of the brain stem
- midbrain
- responsible for vision, hearing and motor control - Pons
- pneumotaxic centre - medulla oblongata
- cardiac centre, respiratory, vasomotor centre, vomiting
-anyhting in the blood stream can be detected by medulla
medulla is long bit
above it is pons
and bit at the top is the midbrain
describe what the ventricular system is made up of
ventricular system:
- 4 interconnected cavities (2 lateral ventricles, a third and a fourth, one in each ventricle)
- CSF produced by choroid plexus found within ventricles
describe what meninges are and the three different membranes
= are the three layers of tissue that protect the brain and spinal cord
- Dura mater
- the tough, outer layer
- ‘skull cap’ - arachnoid
- under the dura
- ‘spider web’ layer - Pia mater
- thin, inner layer
- closely adhered to surface of CNS
what is the subarachnoid space?
= the space between the arachnoid and pia mater meninges, is filled with CSF
describe the spinal cord structure and function
structure:
- tube like structure composed of grey(inner) and white(outer) matter
Grey Matter: Central canal, neuron cell bodies.
White Matter: Axon tracts, ascending/descending pathways.
function:
- communication between brain and body
- communicates via spinal nerves
- when brain is not involved -> reflexes
describe the spinal cord segmentations
- 31 spinal cord segments which each segment having a pair of spinal nerves (left and right)
Cervical(C1-C8) = 8 segments
Thoracic(T1-T12) = 12 segments
Lumbar(L1-L5) = 5 segments
Sacral(S1-S5) = 5 segments
Coccygeal (Co) = 1 segment
from top of spine to bottom:
cervical -> thoracic -> lumbar -> sacral -> coccyx
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describe the structure of the grey and white matter of the spinal cord
grey matter =
- dorsal horn( sensory)
- ventral horn(motor)
- central canal (CSF) in the intermediate zone
white matter =
- dorsal columns (ascending sensory axons)
- ventral columns (descending axons)
- lateral columns (asending and descending)
describe the classification of neurons
- by neurite number
- Unipolar: 1 axon, no dendrites.
Bipolar: 1 axon, 1 dendrite.
Multipolar: Many dendrites, one axon.
pseudounipolar; one axon that splits into branches - dendritic tree structure
Pyramidal (triangular shape, long apical dendrite) vs. Stellate (star-shaped). - axon length
- Projection Neurons (long axons, e.g., pyramidal) vs. Local Circuit Neurons (short axons, e.g., stellate). - the neurotransmitter the neuron releases
- Cholinergic (ACh), Glutamatergic (Glutamate), GABAergic (GABA), Dopaminergic (Dopamine), etc.
Afferent, Interneurons & Efferent Neurons
connections
- sensory(afferent) neurons:
- carry signals to CNS from body (pain, touch) - interneurons
- connect neurons in CNS (form neural circuit) - motorneurons (efferent)
- carry signals from CNS to muscles (movement control)
describe the basic spinal cord circuitry
Dorsal Root: Sensory afferents enter.
Ventral Root: Motor efferents exit.
Spinal Nerves: Mix of afferent & efferent fibers (PNS).
integrating center = regions within CNS that relay impulses from sensory to motor neurons
describe the membrane properties and potential difference
properties:
- acts as a barrier with a hydrophobic core(tails) and hydrophilic(heads) to control ion movement
- hydrophobic acts as a barrier to water soluble substqnces between ICF and ECF
potential difference = the difference in electrical charge across the membrane
- measure inside and outside the cell with a resting of -70mV in neurons
- crucial for cell function
- measured by placing electrode inside the cell and bath electrode outside the cell
- Maintained by ion gradients (e.g., more Na⁺ outside, more K⁺ inside).
how is the membrane potential established?
key factors:
- ion gradients
- selective permeability
- electrochemical gradient (drives ion movement)
- more charge = more potential
equilibrium potentials:
K+ alone = -90mV
Na+ alone = +60mV
Resting membrane potential (-70) closer to K⁺’s due to higher permeability.
action potential generation
- triggered by a stimulus (NT, chemical, physical pressure
- Depolarization - voltage gated Na+ opens, Na+ influx into cell
- if threshold is reached -55mV -> action potential
- hyperpolarization- membrane potential becomes more negative before returning to resting
what is action potential propagation?
= process of action potential travelling along a neuron
unmyelinated axons = continuous conduction
myelinated axons = saltatory conduction (faster jumps at node of ranvier)
what are the two types of potential changes
- graded potentials
- act as short-distance signals/ die over short distance - action potentials
- act as long-distance signals
describe the action of the ligand gated sodium channels
- ligand binds to sodium channels on the membrane
- allows small influx of sodium at these particular channels
- gates close inside the cell to prevent further binding
- this is automatic and rapid and creates an action potential
- ligand is then removed/ broken down outside the cell
describe graded potentials
- occurs in area of the membrane that is active
- magnitude depends on extent of the stimulus
- flow is between the active area and the adjacent inactive area
- short-distance, local membrane change
- die out unless summated
- can be inhibitory (IPSP) or excitatory (EPSP)
what is the name for an individual graded potential from a synapse
= excitatory post-synaptic potential (EPSP)
describe the types of summation
spatial = impulses from several neurons at the same time
- eg more synpases firing simultaneously -> large depolarisation
temporal = several impulses from one neuron over time
- eg one synpase repeatedly firing -> large depolarisation
summation = adding together of stimuli
- if enough EPSPS add together -> threshold potential is reached -> action potential occurs
- temporal must occur for spatial to occur
what are the two types of synaptic transmission
Electrical synapses: Direct ion flow via gap junctions (fast, bidirectional).
chemical transmission (most common)
- neurotransmitter mediated
- slower, more controlled
describe the step by step process of an action potential
- resting state (-70)
- Voltage-gated Na⁺ and K⁺ channels closed.
Na⁺/K⁺ pump maintains resting potential (3 Na⁺ out, 2 K⁺ in).
Inside: negative compared to outside.
Na+ inactivatioj gate is open - Depolarisation (-70 -> +35mV )
- Threshold (-55mV) reached due to graded potentials (EPSPs).
-Voltage-gated Na⁺ channels open → Na⁺ influx.
-Membrane becomes more positive. - Peak depolarization (+35mV)
- Na⁺ channels inactivate (inactivation gate closes).
-Voltage-gated K⁺ channels open → K⁺ efflux. - Repolarisation (+35mV → -70mV)
- K⁺ leaves the neuron → inside becomes more negative.
-Restores negativity but overshoots. - Hyperpolarization (-90mV)
-K⁺ channels stay open longer than needed.
-Membrane potential dips below resting. - Return to Resting Potential (-70mV)
-Na⁺/K⁺ pump restores ion gradients.
-Ready for the next action potential.
describe the step by step process of chemical synaptic transmission
- Action Potential Arrives at Axon Terminal
AP reaches the presynaptic terminal.
Voltage-gated Ca²⁺ channels open. - Calcium Influx (Ca²⁺)
Ca²⁺ enters the presynaptic neuron.
Triggers vesicle fusion with membrane. - Neurotransmitter Release
Synaptic vesicles release neurotransmitter (NT) via exocytosis.
NT diffuses across the synaptic cleft. - Neurotransmitter Binds to Postsynaptic Receptors
NT binds ligand-gated ion channels on the postsynaptic neuron.
Opens Na⁺, K⁺, or Cl⁻ channels. - Postsynaptic Potential (EPSP/IPSP)
Excitatory (EPSP): Na⁺ influx → Depolarization.
Inhibitory (IPSP): K⁺ efflux or Cl⁻ influx →
Hyperpolarization. - Neurotransmitter Removal
Enzyme breakdown (e.g., AChE breaks down acetylcholine).
Reuptake (e.g., serotonin reuptake transporters).
Diffusion away from the synapse.
what is an EPSP
= excitatory postsynaptic potential
- a change in the voltage of a post synaptic cell membrane
-caused by influx of positively charged sodium into the cell - EPSPs combine to exceed the threshold
- are graded potentials that affect the area around a synapse
- brings the cell closer to threshold
- arrive via dendrites
what is hyperpolarization
K⁺ channels stay open a bit too long, causing the membrane potential to dip below resting potential (-90mV).
- before the sodium potassium pump restores it back to resting
what is depolarisation
= when the inside of the cell becomes less negative
why does K+ leave the cell, once Na+ enters through their voltage gated channels?
- Concentration Gradient: There is more K⁺ inside the cell than outside, so K⁺ wants to move out (high → low concentration).
- Electrical Gradient: After Na⁺ influx, the inside is too positive, so K⁺ exits to rebalance charge.
- Selective Ion Channels: Voltage-gated K⁺ channels open at +35mV, allowing rapid efflux. (repolarization/ falling phase)
-> Repolarization resets the neuron, so it can fire another action potential.
what are the factors that impact nerve impulse speed and explain them
- axon diameter
-the larger the diameter, slower the impulse - whether the axon is myelinated or unmyelinated
- myelinated fibres are faster
what is saltatory conduction?
- occurs in myelinated fibres
- propagates action potential 50 times faster than continuous conduction
- impulse jumos from node to node, skipping over myelinated sections
- voltage gated channels are located at the nodes of ranvier as this is where the action potential takes place
why are electrical potentials fast?
- ## an action potential in one cell can produce an almost instantaneous electrical potential in the neighbouring cell
where are gap junctions found
= in areas where you want synchronous activity of neurons
- is a direct channel from the cytoplasm of two cells
what is an IPSP
= if binding of a NT opens either K+ or Cl- channels the result is a small hyperpolarization called an inhibatory-post synaptic potential
- means the cell will be less likely to reach threshold
- arrive via dendrites
what happens if excitatory and inhibitory activity is balanced?
= the membrane potential remains close to resting
- it’s this balance between all inhibitory and excitatory input which will determine if a neuron fires its own action potential
what is the role of the sodium potassium pump
The sodium-potassium pump (Na⁺/K⁺ ATPase) actively transports 3 Na⁺ out of the cell and 2 K⁺ in, using ATP to maintain the ion gradients essential for the resting membrane potential.
This pump works against the concentration gradients of Na⁺ and K⁺ to keep high Na⁺ outside and high K⁺ inside, which is necessary for action potential generation, using ATP.
describe the functional organization of the nervous system
Central Nervous System (CNS) – Brain & spinal cord; processes and integrates information.
Peripheral Nervous System (PNS) – All nerves outside CNS; transmits signals between CNS and body.
Sensory (Afferent) Division – Sends sensory input to CNS.
Motor (Efferent) Division – Sends CNS output to muscles and glands.
Somatic NS (Voluntary) – Controls skeletal muscles.
Autonomic NS (Involuntary) – Controls smooth/cardiac muscles and glands.
Sympathetic (Fight or Flight)
Parasympathetic (Rest and Digest)
describe the functions of the frontal lobe
- prefrontal cortex
- problem solving, complex planning, personality, executive functions - motor cortex
- planning, control and execution of voluntary movements
- is split into:
- Primary Motor Cortex (M1) (Precentral gyrus)
- Premotor Cortex
- Supplementary Motor Area - Broca’s area
- production of speech
- found in left hemisphere
- brocas aphasia is problems with speech generation
- largest lobe
describe the functions of the parietal lobe
- processing of sensory information
two areas:
- primary somatosensory cortex(S1/postcentral gyrus)
- Receives sensory input from skin, muscles, and joints (touch, pain, temperature).
-Organized as a sensory homunculus (larger areas for body parts with high sensitivity, like lips and hands). - posterior parietal cortex
- integration of sensory info
- spatial perception, attention and other cognitive functions
describe the functions of the occipital lobe
- processing visual information
- primary visual cortex (V1)
- located around the calcarine sulcus
- organised into 6 layers each specialized in processing aspects like shape, size, and position.
- also called striate cortex
- receives raw visual data from retina - other areas - V2, 3, 4, 5
describe the functions of the temporal lobe
- processing sensory info, long term memory formation(hippocampus), visual perception and recognition
- auditory cortex
- sound, speech, words, pitch, tone
- located along the lateral sulcus - Wernicke’s area
- language comprehension
- damage causes aphasia-> speak fluent but words are nonsense
describe the key areas in Brodmann’s cytoarchitectural map
- highlights the complexity of the cortex andrelates the structureto it’s function
- each number represents a group of neurons in that area that look the same
17 = primary visual cortex
44 and 45 = Broca’s area
41 and 42 = Wernicke’s area
4 = primary motor cortex
1, 2 and 3 = primary sensory cortex
describe the functional organisation of the peripheral nervous system
- first two main branches are the sensory(afferent) division and the motor (efferent) division
- sensory nerves carry signals to the CNS and motor nerves transmit commands to muscles and glands.
- sensory broken into somatic(receiving sensory info from skin, joints..) and visceral( signals from internal organs)
- motor broken into somatic(voluntary) and autonomic (involuntary)
describe the cranial nerves of the PNS
- 12 pairs arising from the brainstem, and supply head, face and some internal organs with nerves
- can be sensory, motor or both
sensory only:
I - Smell
II - Vision
VIII - Hearing & balance
motor only:
III - Eye movement,
IV - eye movement (4)
VI -eye movement (6)
XI - neck muscles (11)
XII -tongue movement (12)
sensory and motor:
V - Facial sensation + chewing
VII - Facial expression, tears
IX - Taste, swallowing, salivation
X - Vagus: Parasympathetic control of heart rate, lungs, digestion
describe the spinal nerves of PNS
- 31 pairs
- one pair per spinal cord segment
- Each spinal nerve carries both sensory (bring signals to spinal cord) and motor (from spianl cord to muscles) fibers.
Cervical: C1-C8
Thoracic: T1-T12
Lumbar: L1-L5
Sacral: S1-S5
Coccygeal: Co
what are spinal nerve dermatomes?
= Each spinal nerve supplies a specific skin area known as a dermatome.
(sensory regions)
- Exception: C1 has no sensory dermatome.
- named according to spinal cord segment
describe the components of the CNS and PNS interface
Dorsal Root (Sensory Input) – Contains only sensory neurons bringing information to the spinal cord.
Ventral Root (Motor Output) – Contains only motor neurons sending commands from the spinal cord to muscles.
Dorsal Root Ganglion (DRG) – Cluster of sensory neuron cell bodies just outside the spinal cord.
what is a reflex?
Reflexes are rapid, involuntary responses essential for protection and control. They bypass conscious processing
what are the 5 components of a reflex arc
- Receptor – Detects stimulus
- Sensory (Afferent) Neuron – Sends signal to CNS
- Integration Center – Processes input (spinal cord/brainstem)
- Motor (Efferent) Neuron – Sends response signal
- Effector – Carries out response (muscle/gland)
What is the key difference between monosynaptic and polysynaptic reflexes?
Monosynaptic: One synapse between a sensory and motor neuron, no interneurons, very fast (e.g., stretch reflex).
Polysynaptic: Multiple synapses, involves one or more interneurons connecting the sensory and motor neurons, slower but more complex (e.g., withdrawal reflex).
describe the pathway of a knee jerk reflex
- Hammer tap stretches the quadriceps.
- Muscle spindle detects stretch.
- Sensory neuron sends signal to spinal cord.
- Motor neuron sends signal back.
- Quadriceps contract, extending the knee.
how does the withdrawal reflex work?
- Pain receptors activate sensory neurons.
- Interneurons excite motor neurons.
- Flexor muscles contract, withdrawing limb from danger.
What is reciprocal inhibition, and why is it important?
- When one muscle contracts(effector), its antagonist relaxes.
- both starting from same sensory nerve
-Ensures smooth movement & prevents opposition. - Example: In the knee-jerk reflex, quadriceps contract, and hamstrings relax.
What is the function of the crossed extensor reflex?
Works with withdrawal reflex to maintain balance.
Injured side: Flexion (withdrawal).
Opposite side: Extension (supports body weight).
How do autonomic and somatic reflexes differ?
Somatic Reflexes: Involve skeletal muscles (e.g., knee-jerk reflex).
Autonomic Reflexes: Involve smooth muscle, cardiac muscle, glands (e.g., pupil dilation, baroreceptor reflex).
What is the difference between open-loop and closed-loop reflexes?
Reflex removes the stimulus (e.g., muscle stretch reflex).
Open-Loop: Reflex does not remove the stimulus (e.g., withdrawal reflex). (hot plate is not removed, is still there)
describe the enteric nervous system
- branch of the autonomic NS
= controls gut regulation - made up of two layers (myenteric and submucous plexus)
- is a large network of nerves within the walls of the gastrointestinal tract
- can control peristalisis and secretion
- 600 million neurons in GI tract walls.
-Can function independently but influenced by SNS & PNS.
anatomy and functions of the autonomic nervous system
- ## Involuntary control of visceral functions (e.g., heart rate, digestion, breathing).Consists of two neurons which synapse at a ganglion:
1. Preganglionic neuron (from CNS to ganglion) – releases ACh.
2. Postganglionic neuron (from ganglion to target organ) – neurotransmitter varies depending on if it’s sympathetic or parasympathetic (ACh or noradrenaline).
-only the preganglionic neuron is myelinated
compare the parasympathetic and sympathetic pathways in terms of receptors and neurotransmitters
parasympathetic:
- NT released = acetylcholine
- this acts on the muscarinic receptor on the target organ
- postganglionic receptor is nicotinic
- longer preganglionic neuron
- shorter post
sympathetic:
- NT released = mostly noradrenaline
- this acts on adrenergic receptor(alpha or beta) on target organs
- postganglionic receptor is nicotinic
- shorter preganglionic neuron
- longer post
-Preganglionic neurons myelinated, postganglionic unmyelinated → faster impulse in parasympathetic due to shorter unmyelinated neurons.
describe the somatic NS
Controls voluntary movements (skeletal muscles).
Consists of one neuron from CNS to target organ.
Neurotransmitter: Acetylcholine (ACh), acts on nicotinic receptors on skeletal muscles.
Myelinated neurons → faster impulse transmission.
compare the location of preganglionic neurons in parasympathetic vs sympathetic
parasympathetic originates from:
Cranial nerves III, VII, IX, X.
Spinal cord levels S2-S4 (craniosacral outflow).
sympathetic originates from:
- T1-L2 (thoracolumbar outflow).
- specifically the lateral horn
compare the location of the ganglia in parasympathetic vs sympthetic
parasympathetic:
- Cranial nerve X and sacral neurons synapse in ganglia near target organs.
- Cranial nerves III, VII and IX synapse in ganglia in the head
sympathetic:
Sympathetic chain (close to spinal cord).
Prevertebral (pre-aortic) ganglia.
contrast the NT and effects of parasympatheic and sympathetic
sympathetic:
Preganglionic: ACh → nicotinic receptors.
Postganglionic: Noradrenaline → adrenergic receptors.
effects:
increases heart rate & blood pressure.
Dilates bronchi.
Diverts blood to muscles.
Inhibits digestion.
parasympathetic:
Preganglionic: ACh → nicotinic receptors.
Postganglionic: ACh → muscarinic receptors.
effects:
lows heart rate.
Stimulates digestion.
Constricts pupils.
Increases gland secretion.
what is the sympathetic chain?
= a series of ganglia that extend from cranial base to coccyx
- helps to distribute sympathetic neurons by travelling up and down the chains
How can parasympathetic postganglionic neurons cause a decrease in cardiac muscle contraction AND increase in smooth muscle contraction?
= due to differences in muscarinic receptor subtypes and their associated G-protein-coupled receptor (GPCR) signaling pathways.
- different signalling cascades are activated depending on the receptor subtypes
- The location of the receptor and the type of G protein system determine the effect on the target organ when activated.
decrease in cardiac muscle due to M2 receptors(reduce calcium entry)
increase in smooth muscle contraction due to M3 receptors(more calcium entry)
the same neurotransmitter can cause these effects
describe the baroreflex to control blood pressure in terms of the sympathetic and parasympathetic NS
fI blood pressure is too high → Special sensors (baroreceptors) detect this and send signals to the brain.
-The brain activates the parasympathetic system, which slows the heart down and reduces blood pressure.
-If blood pressure is too low → The brain reduces parasympathetic activity and increases sympathetic activity, making the heart beat faster and stronger to raise blood pressure.
importance of ANS in disease
- because of its role in maintaining homeostasis is implicated in the mechanisms underlying many different diseases such as:
- hypertension
- heart failure
- obesity
- depression
- alzheimers
- inflammation
Describe the adrenal medulla and its actions involving the fight or flight response
The adrenal medulla (inside the adrenal gland) is like a special version of a sympathetic ganglion.
Instead of using a second neuron, sympathetic neurons directly stimulate adrenal cells, which release adrenaline and noradrenaline into the blood.
These hormones spread all over the body and activate adrenergic receptors, helping with:
Increased heart rate
Widening airways (bronchodilation)
More blood sent to muscles
Higher energy availability
This fight-or-flight response lasts longer because the bloodstream doesn’t break down adrenaline quickly(no enzymes for this), unlike a normal nerve signal.
describe the manipulation of the ANS in pharmacology
3
- Muscarinic Antagonists Atropine Blocks parasympathetic activity → Used in surgery, dilates pupils.
- Beta-Blockers (β-Adrenergic Antagonists) Propranolol Lowers heart rate, used for arrhythmias.
- Beta-Agonists (β-Adrenergic Agonists) Salbutamol Bronchodilation → Used for asthma.
