nervous system Flashcards
nervous system function
receives and processes information from sense organs and brings about responses to the information received
nervous system divisions
central and peripheral
what does the central nervous system consist of?
brain and spinal cord
parts of the brain
- cerebrum (cerebral cortex, corpus collosum)
- cerebellum
- medulla oblongata
- hypothalamus
function of CNS
incoming messages are processed, outgoing messages are initiated
structures that protect the CNS
- bone
- membranes called meninges
- cerebrospinal fluid
protection - bones
- cranium - houses brain, part of skull
- vertebral canal
both bones provides strong, rigid structure to protect underlying structures
protection - meninges
- three layers of connective tissues forming membranes
- underneath the bones
- covers the surfers of the brain and spinal cord
three layers of connective tissues forming membranes
- dura mater (outer layer) (durable): tough and fibrous
- arachnoid mater (middle layer): loose mesh of fibre
- pia mater (inner layer): delicate, contain blood vessels and sticks closely to the surface of the brain’s and SC, needs lot of oxygen
cerebrospinal fluid location and description
- occupies space between the middle and inner layers of meninges
- circulates through cavities of the brain and canal in centre of the spinal cord
- clear, watery fluid contain a few cells and some glucose, protein, urea and salts
CSF functions (3)
PST
- protection: shock absorber (cushion blows to CNS)
- support: brain is suspended inside cranium, floats in surrounding fluid
- transport: csf formed from blood, csf circulates around and through CNS before re-entering blood capillaries, takes nutrients to the cells of brain and SC, carries away waste
what is the cerebrum
biggest part of brain
cerebrum consists of:
- outer surface = cerebral cortex, thick grey matter = neuron cell bodies, dendrites and unmyelinated axons
- below the cortex, white matter = myelinated axons (myelin gives the white layer is colour and textures
- deep inside cerebrum = basal ganglia (not often discussed). consists of a group of never cell bodies associated with control of skeletal muscles, role in initiating desired movements
cerebral cortex
- vascularised
folded into patterns → greatly increase surface area
70% of all the neurons in CNS
folding produces rounded ridges called convolutions (gyri) separated by sulci (shallow downfolds) or fissures (deep downfolds)
deepest fissure + function
deepest fissure = longitudinal fissure
- separated cerebrum into left and right hemispheres
corpus callosum
corpus callosum joins two hemispheres at base of longitudinal tissue, large bundle of transverse fibres, allows two sides of cerebrum to communicate with each other
how are the cerebral hemispheres divided into lobes?
patterns of folding differs for each oerson
certain fissures and sulci are fairly constant → used to subdivide each cerebral hemisphere into lobes (frontal, temporal, occipital, parietal)
fifth lobe + location
fifth lobe = insula (located deep inside brain)
frontal lobe function
thinking, problem solving, emotions, personality, language, and control of movement
parietal lobe function
processing temp, touch, taste, pain and movement, body orientation
temporal lobe function
processing memories and linking them with senses, receiving auditory info, language comprehension
occipital lobe function
vision (visual reception and interpretation)
insula
recognition of different senses and emotions, addiction and psychiatric disorders
where are all impulses from sensory organs are carried to?
cerebral cortex
cerebral cortex can be divided into three functional areas
SAM
- sensory areas: receives and processes impulses from the senses
- motor areas: send impulses to muscles for voluntary movement
- association areas: interpret information from the senses and make it useful
bundles of nerve fibres (names)
- within CNS, bundles of nerve fibres are called tracts
- outside CNS, bundles of nerve fibres held together by connective tissue are called nerves
between the cerebral cortex and basal ganglia is…
between the cerebral cortex and basal ganglia is white matter composed of nerve fibres
nerve fibres are surrounded by…
surrounded by sheath of white fatty material called myelin
three types of tracts occur in white matter
- tracts that connect various areas of the cortex within the same hemisphere
- tracts that carry impulses between the hemispheres
- tracts that connect the cortex to other parts of CNS
cerebellum location
lies under the rear part of the cerebrum
cerebellum structure (inside and outside)
surfaces is divided into a series of parallel ridges
- outer folded part = grey matter
- inside = white matter that branches to all paths of cerebellum
role: cerebellum
- control over posture, balance and fine coordination of voluntary muscle movement
- receives sensory info from:
- inner ear (info about posture and balances
- stretch receptions in the skeletal muscles info about length of muscles
- all functions offer below conspicuous level
hypothalamus location
middle of brain
hypothalamus function
- controls bodily activities
- homeostasis: maintaining a constant internal environment
- functions include regulations: autonomic NS (hr, bp, secretions of digestive juices, movements of alimentary canal, dilation of pupil), body temp, food and water intake, patterns of waking and sleeping, contractions of the urinary bladder, emotional responses, secretion of hormones
medulla oblongata
- continuation of SC
- nerve fibres pass through the medulla going to or from other parts of the brain
what does the medulla oblongata contain?
- cardiac centres: regulate rate and force of the heartbeat
- respiratory centres: control rate and depth of breathing
- vasomotor centre: regulates the diameter of blood vessels
- other centres regulate reflexes of swallowing, sneezing, coughing and vomiting
spinal cord length
- 44cm long in adults
- Extends from foramen magnum (large opening at base of skull) → second lumbar vertebrae
how is spinal cord heavily protected?
Cord enclosed in vertebral canal
what are inside ring of bone (spinal cord)
three meningeal layers
- Outer layer isn’t joined to bone like in the skull
- instead, Space containing fat, connective tissue and blood vessels serves as padding around SC and allows cord to bend when spine is bent
grey matter
nerve cell bodies and unmyelinated nerve fibres
white matter
myelinated fibres
grey and white matter of the SC
Grey matter of the SC is at the centre, surrounded by white matter
Myelinated fibres of white matter arranged in
bundles
Grey matter is roughly the shape of letter H
central canal
In cross bar of the H is small space called the central canal
Runs length of SC and contains CSF
ascending tracts
Sensory axons that carry impulses upwards towards the brain
descending tracts
Motor axons that conduct impulses downwards, away from the brain
function of spinal cord
- carry sensory impulses up to the brain, and motor impulses down from the brain
- Integrate fast, autonomic responses called reflexes
peripheral nervous system function
- takes messages from receptors → CNS
- from CNS → muscles and glands
PNS composed of:
- Nerve fibres that carry info to and from the CNS
- Groups of nerve cell bodies called ganglia which lie outside of the brain and spinal cord
nerves
Nerve fibres arranged into nerves which arise from the brain and spinal cord
types of nerves
cranial nerves and spinal nerves
cranial nerves
- 12 pairs that arise from the brain
- most are Mixed nerves = contain fibres that carry impulses into the brain, and fibres that carry
impulses away from the brain- Sensory fibres = carry impulses into CNS
- Motor fibres = carry impulses away from CNS
Spinal nerves
- 31 pairs arise from SC
- All are mixed nerves containing both sensory and motor fibres
- Each nerve is joined to the SC by two roots
- Ventral root = axons of motor neurons that have cell bodies in the grey matter
- Dorsal root = axons of sensory neurons that have cell bodies in the dorsal root ganglion (big boy)
DIVISIONS OF THE PERIPHERAL NERVOUS SYSTEM
sensory (afferent): conducts signals from receptors to CNS
motor (efferent): conducts signals from CNS to effectors
motor (efferent) DIVISIONS OF THE PERIPHERAL NERVOUS SYSTEM
Autonomic nervous system and Somatic nervous system
Autonomic nervous system
Controls body internal environment
Operates without conscious control (involuntary)
Regulated by groups of nerve cells in the medulla oblongata, hypothalamus and cerebral
cortex
how does impulses travel controlled by the ANS? (Examples of body functions regulated by Autonomic NS)
- Nerve fibres make up part of the spinal nerves and part of some of the cranial
nerves - Carry impulses to the heart muscle, other muscles of internal organs and the glands
- The impulses travels along two neurons from the CNS to an organ controlled by the ANS
- first neuron = myelinated and has its cell body in the CNS
- Second neuron = unmyelinated and has its cell body in a ganglion
difference between autonomic and
somatic divisions
Pathway from CNS → heart muscle, involuntary muscle or glands
Autonomic pathway
two motor neurons involved (involuntary)
Somatic pathway
one motor neuron carrying impulses from CNS → effector (voluntary)
subdivisions of autonomic nervous system
sympathetic and parasympathetic
sympathetic division + neurotransmitters released
prepares the body for strenuous activity
fight or flight response
Neurotransmitters released: noradrenaline/norepinephrine
parasympathetic division
maintain the body during quiet conditions
Neurotransmitters released: acetylcholine
sensory (afferent) division subdivisions
somatic and visceral
Fight or flight response
- When calm = sympathetic and parasympathetic nerves send out impulses to internal
organs to maintain stability of body functions - In threatening situation = sympathetic becomes more dominant
- Fear, anger, stress, danger or competition → fight or flight
- Prepare the body for increased activity
- Increased level of alertness to think and act quickly
- Require greater supply of oxygen and glucose → increased blood flow to relevant structures
neurons
NERVE CELLS
- Basic structural and functional units of the whole nervous system
- Highly specialised cells designed for rapid communication of messages in body
- Vary in size and shape
synapse
junction between two neurons (one’s axon terminals and the other’s dendrites
Messages have to be carried across this gap
how do nerve impulses travel
neuron to neuron
how are messages carried across a synapse?
Occurs by movement of chemicals called neurotransmitters
neuromuscular junction
Where axon meets skeletal muscle cell
types of neurons (3) based on function
- SENSORY/AFFERENT/RECEPTOR NEURONS
- Carry messages from receptors in sense organs or skin → CNS
- MOTOR/EFFERENT/EFFECTOR NEURONES
- Carry msgs from CNS → effectors (muscles and glands)
-INTERNEURONS/ASSOCIATION NEURONS/RELAY/CONNECTION - Located in CNS
- Link b/w sensory and motor neurons
- Carry msgs from CNS → effectors (muscles and glands)
types of neurons (4) based on structure
MULTIPOLAR NEURONS
BIPLOAR NEURONS
UNIPOLAR NEURONS (insects only)
PSEUDOUNIPOLAR
multipolar neuron
- One axon and multiple dendrites
- Most common (most of the interneurons in the brain and SC, and motor neurons)
bipolar neurons
- One axon and one dendrite
- Occur in the eye, ear and nose
- Take impulses from receptor cells → other neurons
unipolar neurons
- One axon
- Not found in humans – but insects
pseudounipolar neurons
- Properties of both unipolar and bipolar
- Single axon which separates into two extensions
- One extension connects to dendrites
- Other to axon terminals
- Cell body lies to one side of the main axon
- Most sensory neurons that carry msgs → SC
NERVE FIBRES
any long extension of cytoplasm of a nerve cell body
- Axons and dendrites of nerve cells = nerve fibres
- Arranged in bundles held together by connective tissue
- Multiple bundles joining together → nerve (outside CNS)
axon
long extension of cytoplasm
carries nerve impulses away from cell body
cell body/soma
contains nucleus
responsible for controlling functioning of cell
dendrites
extension of cytoplasm of cell body
carry messages into cell body
myelin sheath
layer of fatty material
acts as an insulator
protects axon from damage
speeds up movement of nerve impulse along axon
node of ranvier
intervals along axon
facilitates rapid conduction of nerve impulses
axon terminals
release neurotransmitters into synapse
schwann cells
cells that produce myelin sheath
nerve impulse
-
Electrochemical change that travels along a nerve fibre
- Electro - Change in electrical voltage
- Chemical - Brought about by changes in chemicals (conc. Of ions inside and outside the cell membrane of the neuron)
nerve impulses are transmitted quickly so…
it Allows body to respond rapidly to any changes in internal and external environment
Electrical change and potential difference
Two types of charges = +ive and –ive
* +ive and +ive OR –ive and –ive = repel!
* +ive and –ive = attract!!
- Opposite charges are separated, electrical force pulls them together
- That force can be measured, and it’s strength increase as the charges get closer and larger
- +ive and –ive charges come together → energy released
- +ive and –ive charges are separated, they have potential to come together and release energy
Potential difference measurement
Potential difference b/w two places can be measured (voltage V or mV)
when chemical substances dissolve in water, they….
- they break up into electronically charged particles (ions)
- Happens to some of the substances dissolved in the fluid around and inside cells
extracellular fluid + conc
- (outside cell) = high conc. of sodium chloride (NaCl)
- Most of its charged particles are sodium ions (Na+) and chlorine (Cl-) ions
intracellular fluid
- (inside cell) = low conc. of Na+ and Cl- ions
- Most of it’s charge particles are potassium (K+) and variety of negative organic ions
Differences in the conc. of ions means…
there is a potential between the inside and outside of the cell membrane
membrane potential + rmp
- Occurs in all body cells; large in nerve and muscle cells
- Unstimulated nerve cells (resting membrane potential) = -70mV
- Potential of the inside of the membrane is 70mV less than the outside
- Fluid inside cell is more negatively charged than fluid outside
- Potential of the inside of the membrane is 70mV less than the outside
ions unable to diffuse through the phospholipid bilayers of cell membrane Move through… +diff types of these
protein channels
- Leakage channels (open all the time)
- Voltage-gated channels (open only when nerve is stimulated)
Resting membrane potential of neurons is due to…
differences in distribution of K and Na on either side of the cell membrane
rmp charge comparison between intercellular and extra cellular fluid
- Extracellular fluid more +ively charged than intracellular
conc of Na at rmp + why
- Conc. of Na+ higher outside the neuron
- Cell membrane only slightly permeable to Na+ due to limited number of sodium leakage channels (limits facilitated diffusion of Na+)
conc of K at rmp + why
- Conc. of K+ is greater inside the neuron than outside
- Cell highly permeable to K due to larger number of K leakage channels (more K ions are able to diffuse than Na)
conc of Cl at rmp
- Conc. of Cl- ions is higher outside of neuron than inside
- Cell membrane is highly permeable to Cl- ions → allowing their diffusion through protein channels
conc of negatively charged organic ions at rmp
- Conc. of large, negatively charged organic ions is higher inside the neuron than outside
- Cell membrane is impermeable to these ions → stay inside the cell
how do Na+ and K+ ions move through cell membrane?
through a carrier protein
known as the sodium-potassium pump
how does sodium-potassium pump work
- Moves 2 K+ → cell for every 3 Na+ that are removed
- Net reduction of +ions inside the cell
- Movement against the concentration gradient = active transport and uses ATP
- Concentration gradient = concentration of particles is higher in one area than another
many causes of net flow of +ive ions out of the cell
Combination of:
- Location of ions
- Permeability of the cell membrane
- Sodium-potassium pump
- More K+ diffusing out of the cell than there are Na+ ions diffusing in
- Negative organic ions inside cell → inside of cell being more –ive than outside
- Produces a negative resting membrane potential → membrane is polarised
how is resting membrane potential is maintained?
The resting membrane potential is maintained by a difference in the no. of leakage channels for Na and K ions, membrane being impermeable to large organic –ive ions and sodium-potassium pump. Intracellular fluid = less +ively charged than the extracellular fluid
action potential (conduction of nerve impulse)
If stimulus to a neuron is sufficient, signal will be passed along the neuron
- Happens due to opening and closing of voltage-gated channels → rapid depolarisation and repolarisation of the membrane
- Lasts 1 millisecond and is called an action potential
depolarisation
- Sudden increase in membrane potential
- Occurs if the level of stimulation exceeds 15mV or the threshold
- When a neuron is stimulated by a neurotransmitter/sensory receptor, some Na channels
open- Channels known as ligand-gated channels
- Once they are opened, more Na+ move into the cell → makes extracellular fluid less –ive,
increasing the potential difference
- If stimulus is strong enough to increase the potential to -55mV, then voltage-gated sodium channels open
- Produces a movement of Na+ into the cells (size of response not related to the strength of the stimulus) = all-or-none response
- Inward movement of Na+ is too great to be balanced by an outward movement of K+, making the inside of the membrane more +ive than the outside
- Original polarity of the membrane increases → 40mV
- Membrane is depolarized = no difference in electrical charge b/w inside and outside of membrane
repolarisation
Occurs after a short period
Sodium channels close → stops influx of Na+
Voltage-gated K+ channels open, increasing the flow of K+ out of the cell
- Makes the inside of the membrane more –ive than the outside → decreases the membrane
Potassium channels remain open longer than what is needed → membrane potential
decreasing lower than resting membrane potential→membrane is hyperpolarized
refractory period
Once sodium channels have opened, they quickly become inactivated (unresponsive to stimuli)
- For a brief period after being stimulated, the membrane will not undergo another action
potential = refractory period- Lasts from when the membrane reaches the threshold of -55mV until it returns to the resting membrane potential of -70mV
simple terms: transmission of nerve impulse along nerve fibre
- Sodium ions diffuse into cell
- Inside of cell becomes positive relative to the outside
- Potassium ions diffused out of the cell
- Inside of the cell becomes negative relative to the outside
transmission of the nerve impulse
Single action potential occurs in one section of a membrane, but triggers action potential in the adjacent membrane
- Continues along the length of the neuron = nerve impulse
Action potential doesn’t travel along the nerve fibre; it is the message/nerve impulse that travels along the fibre
Transmission along myelinated fibres
- Myelin sheath insulates the nerve fibre from extracellular fluid
- Where the nerve fibre is surrounded by myelin, ions cannot flow b/w inside and outside
of the membrane → AP cannot form - Instead, AP jumps from one node of Ranvier to the next
saltatory conduction allows for?
Saltatory (jumping) conduction allows the nerve impulse to travel much faster along myelinated fibres than unmyelinated ones
- Myelinated = 140m/s
- Unmyelinated = 2m/s
Size of the nerve impulse + how to determine strength of stimulus
- nerve impulse that travels along a fibre is always the same size regardless of size of
stimulus- Weak stimulus (provided it exceeds the threshold) produces the same AP as a strong one (all
or none response) - Magnitude of impulse always the same
- Weak stimulus (provided it exceeds the threshold) produces the same AP as a strong one (all
- two things enable us to determine the strength of a stimulus
- Strong stimulus causes depolarization of more nerve fibres
- Strong stimulus produces more nerve impulses in a given time than a weak stimulus
TRANSMISSION ACROSS A SYNAPSE
- Nerve impulse reaches axon terminal, activates voltage-gated calcium ion channels
- Higher conc. of calcium ions in the extracellular fluid → flow into cell at pre-synaptic axon
terminal - Causes synaptic vesicles to fuse with membrane, releasing neurotransmitters by exocytosis
- Neurotransmitters diffuse across the gap → attach to receptors on the membrane of next
neuron - Stimulates ligand-gated protein channels to open → allows influx of Na+ and initiates AP in
post synaptic membrane
how are neurotransmitters removed from the synapse?
Neurotransmitters removed from the synapse by being reabsorbed by the presynaptic membrane
- Degraded by enzymes or moving away through diffusion
examples of neurotransmitters
acetylcholine, adrenaline, dopamine and histamine
EFFECT OF specific CHEMICALS ON THE TRANSMISSION at synapse and neuromuscular junction
Natural and synthetic chemicals influence the transmission of nerve impulses
- At the synapse
- Stimulants (caffeine) stimulates transmission at the synapse
- Anaesthetics or hypnotics depress the transmission
- At the neuromuscular junction
- Venom
Receptor
structure that is able to detect a change in the body’s internal or external environment
stimulus
any external or internal change that causes a response
sense organ: receptors
- Receptor cells of a particular type are group together in a sense organ
- Light receptors in the eye
- Receptors sensitive to sound vibrations in the ear
reason for different receptors
Changes in environments come from different sources
thermoreceptors
- Located in the skin
- Able to respond to heat and cold
- Examples
- Skin thermoreceptors inform the brain of changes in the temp
- Peripheral thermoreceptors in the skin are nerve endings that are sensitive to heat or cold
Temperature inside the body (core temperature) is monitored by thermoreceptors in the hypothalamus
- detect the temperature of blood lowing through brain
osmoreceptors
Sensitive to osmotic pressure of body fluids
- Osmotic pressure = determined by the conc. of substances dissolved in the water of the
blood plasma - Higher the conc., the greater the osmotic pressure
- Located in the hypothalamus
- can stimulate the hypothalamus so that the body’s water content is maintained in narrow limits
chemoreceptors
Stimulated by chemicals
Nose = sensitive to odours
Mouth = sensitivity to taste
Internal chemoreceptors sensitive to composition of body fluid
- Receptors in blood vessel sensitive to the pH of blood and the conc. of oxygen and carbon dioxide
- Involved in the regulation of HR and breathing
TOUCH RECEPTORS/MECHANORECEPTORS/PRESSURE RECEPTORS
Found in the skin
- Different types
- Some close to the surface of the skin; sensitive to light tough eg. Lips, fingertips, eyelids
- Some are deeper in skin; sensitive to pressure and vibrations
pain receptors + location
- Stimulated by damage to tissues
- Cut or heavy bump
- Poor blood flow to a tissue
- Excessive stimulation from stimuli such as heat or chemicals
- Concentrated in the skin and mucous membranes
- Occur in most organs, but not the brain
- Essential for our wellbeing
- Warns us that damage to tissues is occurring so we can take action
- Don’t adapt well – so pain will continue as long as stimulus is present
location of receptors
Many receptors located deeper in dermis
Pain receptors are in the epidermis
- Closer to the surface of the skin
- Detects change more quickly to help prevent damage!
reflex
rapid, autonomic response to a change in the external or internal
environment
Four properties of a reflex
SIRS
- Stimulus is require to trigger a reflex
- Reflex is involuntary (occurs without conscious thought)
- Response is rapid (small number of neurons are involved)
- Response is stereotyped (occurs in the same way each time it happens)
what are most reflexes coordinated by?
spinal cord
reflex arc
Pathway a nerve impulse follows in travelling from a receptor → effectors
Purpose of spinal reflex arc
protect body from harm
spinal reflex: describe
- Involuntary (even though it may involve contraction of skeletal muscles)
- Impulses are sent to the brain so we are aware of whats happening, but awareness doesn’t occur until after the response has been initiated
reflex arc components + role
receptor: reacts to a change in the internal or external environment by initiating a nerve impulse in the sensory neuron
sensory neuron: carries impulse from receptor to sc and brain
synapse: nerve impulse may be passed directly to a motor neuron or there may be an interneuron that directs the impulse to the correct motor neuron
motor neuron: carries nerve impulse to effector
effector: receives the nerve impulse and carries out appropriate response
examples of effectors
muscle cells or secretory cells
learnt reflexes
Protective reflexes (eg. secretion of saliva in response to sight, smell, taste of
food) are present from birth
- Suckling, chewing = innate reflexes
Some complex motor patterns are learnt and called acquired reflexes
- Muscles adjustments required to maintain balance whilst riding a bike
- Learnt through constant repetition
parkinson’s disease: desc, cause, symptoms and cell replacement therapy
loss of neurons in brain
cause: reduced dopamine lebels hence damage/degeneration to nerve cells in the brain
symptoms:
tremors, slowed movement, rigid muscles, speech changes
cell replacement therapy: replacement of cells using stem cells that establish connection with adjacent neurons
alzheimer’s disease
brain shrinks and brain cells to die
cause: tangles of tau protein and plaques from clusters disrupt work of neurons hence brain cells die
symptoms:
memory loss, thinking and reasoning, personality and behavioural changes
cell replacement therapy: replacement of cells using stem cells that find inflammation and repair it
