B3.1 Nervous System Flashcards
Function of nervous system
To detect changes in the environment and respond to these changes to maintain homeostasis
Name given to change in environment
Stimulus
Name group of cells responsible for detecting a stimulus
Sensory receptors
Where are receptor cells generally found
Sense organs
Some common examples of sense organs and their stimulus (5 senses)
Eye - Light
Tongue - Chemical tastes (in food and drink)
Nose - Chemical smells (in the air)
Skin - Temperature, pressure and pain
Ears - Sound
Name given to cells that carry out the response
Effectors
2 types of effectors giving an example response for each
Muscles - respond by contracting
Glands - respond by secretions
2 key components of the nervous system
Central nervous system (CNS)
Peripheral nervous system (PNS)
Key components of nervous system
Brain
Spinal cord
Nerves
Central nervous system
Composed of brain and spinal cord
Brain is only involved in voluntary actions
Involved in both voluntary and involuntary actions
Peripheral nervous system
PNS is composed of nerve cells that carry information to and from CNS in spinal cord
Invovled in both voluntary and involuntary actions
3 main types of nerve cell including their pathway
Sensory – neurones that carry information as electrical impluses from receptors in the sense organs to CNS
Relay – neurones that carry electrical impulses from sensory neurones to motor neurones, found in CNS
Motor – neurones that carry electrical impulses from CNS to effectors
Direction of impulse
Direction in which a signal travels through a nerve
Type of signal is transmited by nervous system
Electrical
Difference between nerve and neurone
Neurones = specialised cells that conduct electrical impulses through body
Nerve = bundle of many nerve fibres enclosed within a protective sheath
Nerve fibres = long axons of neurones together with any associated tissues
Pathway for a ‘voluntary action’
Stimulus → Receptor cells → Sensory neurone → Spinal cord → Brain → Spinal cord → Motor neurone → Effector → Response
What is menat by a ‘coordinated’ response
Ability of brain to process information from many sensory receptors simultaneously and send a series impulses to different parts of the body to produce the required actions
Direction of impulse through neurone with reference to labels
. Y ]1 3
>-★-<===-<-< ]4
I
2
Impulse travels from dendrites (1) through neurone to axon terminals (4)
Parts of a motor neurone
. Y ]1 3 .
>-★-<===-<-< ]4
I
2
1) Dendrites
2) Cell body
3) Axon
4) Axon terminals
Cell type that surrounds axon of certain neurones and their purpose
Schwann’s cells
Collectively they form MYELIN SHEATH - insulates axon and increase speed of transmission
Gaps between these cells = nodes of Ranvier
Synapse
Area between axon terminals of pre-synaptic (previous) neurone, and dendrites of post-synaptic (next) neurone
Synapse aka synaptic cleft
Name to mode of transmission within a synaptic cleft / synapse
Chemical
Pathway of transmision from axon terminals pre-synaptic neurone to post-synaptic neurone
Electrical signal arrives at axon terminals of the pre-synaptic neurone.
Vesicles containing neurotransmitters stimulated.
Neurotransmitters difuse out of pre-synaptic neurone into synaptic cleft.
Neurotransmitters difuse across synaptic cleft.
Neurotransmitters bind to receptors dendrites of the post-synaptic neurone
Electrical signal triggered by neurotransmitters in the post-synaptic neurone
e.g electrical → chemical → electrical
Simple:
The neurotransmitters bind to receptors on the next neurone.
Neurotransmitters diffuse across the synapse.
The presence of the neurotransmitter causes the production of an electrical impulse in the next neurone.
Organelle in abundance in neurones
Mitochondria to provide energy
Difference between voluntary and reflex action
Voluntary actions involve conscious thought
Reflex actions are automatic (involuntary) reactions, they are unconscious missing out the brain, occuring without thinking
Reflex that protects retina in changing light intensities
Pupil reflex
How your body responds to stepping on a sharp object from stimulus to response
Stimulus - stepping on sharp object
Receptor - pressure receptors in the skin
Electrical impulse transmitted through sensory neurone to spinal cord
Electrical impulse transmitted through motor neurone to muscles in thigh of the leg
Effector - the muscles in thigh of the leg lift the leg to move away from the object in response
Cornea
Transparent coating on the front of the eye
Protects eye
Reflects light entering eye
Conjunctiva
Protective membrane continuous with eyelids across front of visible sclera
Protects from infection by stopping pathogens entering eye
Pupil
Central hole in iris
Allows light to enter eye
Iris
Coloured ring of muscle
Alters pupil size by contracting or relaxing
Lens
Transparent BICONVEX lens
Focuses light clearly onto retina
Suspensory ligaments
Work together with the cilary body to control the shape of lens by becoming taught or slack
Connect the ciliary body to lens
When ciliary muscles contract - suspensory ligaments relax - lens goes fat
When ciliary muscles relax - suspensory ligaments are pulled taught - lens gets thinner
Retina
Contains 2 types of photoreceptor cells rods and cones
Photoreceptor cells produce a nervous impulse when exposed to light
Optic nerve
Nervous tissue
Carries nerve impulse / transmits visual information from retina to brain
Parts of eye
Sclera – Tough outer wall, ‘white’
Conjunctiva – membrane over eye
Cornea – transparent outer layer
Lens – focuses light
Pupil – hole in the centre of the iris, through which light passes, allowing light into eye
Aqueous humor - nutrients & pressure
Iris – controls diameter of pupil via circular and radial muscles and the quantity of light reaching the retina.
Vitreous humor – pressure and shape.
Choroid – nutrients & waste
Fovea – blind spot
Optic nerve head – nerves exit
Optic nerve – impulses to eye
Retina – contains rod & cone cells
ciliary muscles are a ring of smooth muscle that changes the shape of the lens to focus light.
suspensory ligaments are a ring of fibres that connect ciliary muscles to the lens
Aqueous humour
Fluid between cornea and lens that provides nutrients for lens and cornea that have no blood supply and helps maintain pressure
Vitreous humor
TRANSPARENT, COLOURLESS, gel-like substance that fills space between LENS and RETINA within the eye and helps maintain pressure and shape
2 types of photo receptor cell in eye
Rods - respond to light and allow you to see in low light levels
Cones - respond to red, blue and green light to allow you to see in different colours
How circular and radial muscles control the size of pupil
In DIM light radial muscles CONTRACT and circular muscles RELAX to make pupil become larger to allow more light to reach retina
In BRIGHT light radial muscles RELAX and circular muscles CONTRACT to make pupil become smaller and protect retina
How suspensory ligaments and cilliary muscles control shape of lens
Nearby object - cilliary muscle contracts down towards the lens - suspensory muscles to become slack - causes the lens to fatten and become more convex - increasing refraction of light passing through lens
Far object - cilliary muscle relaxes away from lens - pulls suspensory muscles taut - causes lens to be pulled thiner and become less convex - decreases refraction of the light passing through
Accommodation (biology)
Process of focusing incoming light by the eye
Myopia
Shortsightedness
Can see near objects clearly,
but they cannot focus properly on distant objects
Eyeball elongated = distance the lens to retina too far
Lens too thick and curved = light is refracted to much and focuses short
Corrected with CONCAVE lens in front of eye
Hyperopia
Longsightedness - length of eyeball too short
Loss of elasticity in the lens = cannot become thick enough to focus (often age-related)
Can see far objects clearly, but they cannot focus properly on near objects
Lens focusses converge of light rays behind retina
Corrected with CONVEX lens
Brain
Process information collected by receptor cells about changes in internal and external environment
Recieves and processes information from hormonal system
Produces a coordinated response for all of the information it recieves
Speeds up neuronal communication by providing a centralised control centre
Approximately how many neurones does an adult brain contain
86 billion
How the delicate nervous tissue of the brain is protected
Protective membranes around the brain
Skull
Cerebrum
LARGEST part of brain, made of cerebral cortex (the 2 folded hemispheres)
Controls CONSCIOUSNESS, LANGUAGE, THOUGHT, PERCEPTION, MEMORY, ATTENTION
Receives input from sensory systems of spinal cord and from other parts of brain, and integrates these inputs to fine-tune motor activity
Several structures underneath the cerebrum, including hippocampus which is involved with memory
Cerebellum
SECOND LARGEST part of brain
Does not initiate movement but contributes to coordination & precision
Cerebellar damage produces disorders in movement, balance, posture, and motor learning in humans
Medulla oblongata
Part of brainstem, involved with UNCONSCIOUS ACTIVITIES - controls:
HEARTBEAT
GUT
RATE + DEPTH OF BREATHING
VOMITING
BLOOD PRESSURE
Pituitary gland
‘Pea-sized’ gland often referred to as the ‘master gland’ which stores and releases hormones
Secretes hormones that act both directly and indirectly
Hypothalamus
Controls ‘thermo’ and ‘osmo’ regulation
Interacts with pituitary gland - links nervous system to hormonal system
How can you investigate brain function
Work out what different areas of the brain do based on what happens when those areas were damaged e.g. stroke victims provide evidence to map the brain
Stimulation with electrodes internally or externally to electrically stimulate the brain while the patient is awake
Computed tomography (CT) scans use X-rays to create 3D images of the brain to detect abnormalities
Functional magnetic resonance imaging (fMRI) uses powerful electromagnets to generate real-time images of brain
Who was involved in an explosion resulting in and iron pole going through his skull in 1848 providing some of the first evidence of the consequences of brain damage?
Phineas Gage (1823-1860)
Pole removed parts of cerebral cortex involved with social inhibition
He suffered behavioural changes
Henry Gustav Molaison (1926-2008)
Had large parts of his hippocampus removed on both sides of his brain to try and treat his epilepsy
After sugery, Molaison suffered profound memory loss
He was able to learn new motor skills after the surgery but not able to learning new information
He only remembered past events
Victor Leborgne (1824-1880)
Nicknamed “Tan” because that was the only word he could say
Brain studied by Paul Broca
Possible causes of nervous system damage
Injury
Disease
Inheritance
Toxins
Possible effects of PNS damage
Inability to detect pain
Numbness
Loss of coordination
Difference between PNS injury and CNS injury
PNS - limited abiliy to regenerate with minor nerve damage often self healing
CNS - cannot regenergate
Effects of CNS damage
Loss of control of body system
Partial or complete paralysis
Memory loss or processing difficulties
Why it is almost impossible to repair damage to the spinal cord
Consists of 31 pairs of nerves, each of which contain many nerve fibre
Only 1.5 cm in diameter therefore it is very difficult to identify and repair an individual nerve
Treatments available for damage to brain
Radiotherapy & chemotherapy for tumours
Surgery to remove damaged brain tissue
Deep brain stimulation to stimulate brain function
Diagram of synapse in a reflex arc
. , 1: relay neurone
,
,,,.
,o,.o. 2: vesicle containing neurotransmitter acetylcholine
3: synapse
,,, *,,, 4: motor neurone
.,,…….,,
,,,,
,,
What happens when ciliary muscles contract
Lens becomes fatter - can focus on near obiects
