UNIT 3: The Human Nervous System Flashcards
central nervous system
composed of the brain and spinal cord
peripheral nervous system
composed of all the nerves not found within the boundaries of the central nervous system as well as the collections of nerve cells called ganglia.
neuron
nerve cell specialised to carry electochemical impulses.
functional unit of the human nervous system
sensory neurons
carry impulses towards the central nervous system
interneurons
carry impulses from one neuron to another completely within the central nervous system
motor neurons
carry impulses from the interneuron to an effector
effector
an organ or tissue that carries out an action in response to a signal from the nervous system
neuron cell components: dendrites
receive impulses from other neurons and transmit the impulse towards the cell body
neuron cell components: cell body
located between the dendrites and axon. it is responsible for the upkeep of the cell and for producing neurotransmitter substances
neuron cell components: neurotransmitter
chemical substance released by a neuron to transmit a nerve impulse to another neuron or effector
neuron cell components: axon
carries impulses away from the cell body towards axon terminals
neuron cell components: myelin sheath
layers of lipids formed from a schwann cell that wrap around the axon and dendrites or neurons. It insulates the axon / dendrite maintaining and speeding up the electrochemical impulse.
neuron cell components: schwann cell
produces myelin sheath
neuron cell components: axon terminals
present at the end of the axon and contain synaptic vesicles which contain neurotransmitters
neuron cell components: synaptic vesicles
contain neurotransmitter chemicals. They fuse with the cell membrane when an impulse reaches the axon terminal. this releases the neurotransmitter
nerve impulse
a short-lived electrochemical signal that travels along neurons via movement of chemical ions into and out of the neuron
transmission of the nerve impulse to another neuron
occurs at synapses
synapses
structure where 2 neurons come into close contact so that a nerve impulse can be transmitted between the 2 neurons
transmission process
- nerve impulse arrives at an axon terminal (presynaptic neuron).
- synaptic vesicles are stimulated to fuse with the cell membrane.
- neurotransmitter chemicals are released from the vesicle into the gap between the 2 neurons, called the synaptic cleft; examples of neurotransmitter substances include: acetylcholine, noradrenaline and dopamine.
- once a neurotransmitter is in the synaptic cleft it travels the short distance to the dendrite of the postsynaptic neuron where it stimulates the cell membrane to allow ions to flow inwards, setting up a new electrochemical impulse.
- the neurotransmitter is then either broken down by enzymes or reabsorbed into the presynaptic neuron.
functions of the synapse
- allow transmission of the impulse from one neuron to another.
- control the direction of the impulse - the impulse cannot travel backwards.
- acts as junction allowing the impulse to be split up and travel along many different neurons or join many impulses together into one impulse
conjunctiva
produces mucous protecting the front of the eye
cornea
transparent part of the sclera that protects the front of the eye; it also allows light tot enter the eye and refracts the light rays slightly as part of focusing light into the retina
iris
coloured part of the eye.
type of smooth muscle that can contract and relax in response to the amount of light entering the eye
pupil
hole in the internal part of the eye just behind the iris. it allows light into the eye and its size is controlled by the iris. it appears black due to light entering and not leaving the eye as it is all absorbed
aqueous humour
watery liquid present just inside the cornea that gives shape to the front of the eye
vitreous humour
viscous liquid present inside the eye ball that maintains the shape of the eye by maintaining outward pressure on the sclera.
ciliary body
type of smooth muscle surrounding the lens that can contract and relax changing the shape of the lens as part of focusing light on the retina
suspensory ligament
attaches to and surrounds the ciliary body providing a lever for the contraction of the ciliary muscle
lens
transparent structure held in place by the ciliary body and suspensory ligament; changes shape in response to contraction and relaxation of ciliary body. responsible for focusing light on the retina
sclera
white of the eye covering the entire eyeball except the front part, protects the eye and acts as the attachment surface for external muscles that move the eye in different directions
choroid
heavy pigmented layer lying between the retina and sclera, absorbs all of the light entering the eye and helps to prevent reflection within the eye
retina
light-sensitive structure of the eye; contains rods and cones; rods are sensitive to only black and white and cones are sensitive to red, green and blue light.
fovea
region of the retina where all of the light rays converge when you look directly at an object, mostly composed of cones
blind spot
region of the retina where all the nerve fibres from the retina converge and exit the eye and travel to the brain; there are no light-sensitive cells in this region
optic nerve
collection of sensory neurons that carry messages to the brain from the retina
long-sightedness (hyperopia): symptom
near objects appear blurred
long-sightedness (hyperopia): cause
eyeball is either too short or the focusing elements are too weak
long-sightedness (hyperopia): treatment
convex lens placed in front of the eye
short-sightedness (myopia): symptom
distant objects appear blurred
short-sightedness (myopia): cause
eyeball is either too long or the focusing elements are too strong
short-sightedness (myopia): treatment
concave lens in front of the eye
outer ear
composed of the pinna and auditory canal.
these pick up sound waves and channel them to the eardrum
middle ear
- the sound waves arrive at the eardrum and are transferred into the 3 small bones of the ear - the ossicles - hammer, anvil and stirrup.
they transfer sound waves onto the inner ear.
they can amplify soft sounds and dampen loud sounds. - the eustachian tube is connected to the throat so that pressure differences can be equalised during swallowing preventing damage to the eardrum
inner ear
functions in both hearing and balance
composed of cochlea & vestibular apparatus
cochlea
- receives sound vibrations from the ossicles via the oval window.
- it is filled with lymph through which the sound waves pass.
- there are hair cells within the inner wall of the cochlea that sense the vibrations of the lymph and convert these vibrations into electrical impulses that are then sent to the brain via the auditory nerve.
- finally, there is a round window below the oval window that vibrates with an opposite phase to the round window allowing vibrations to be transferred within the lymph more efficiently
vestibular apparatus
- consists of 3 semicircular canals filled with lymph.
- each canal has hair cells lining its internal walls.
- as the head moves, the lymph moves within the canals stimulating the hair cells.
- the movement of the lymph is converted into electrical impulses by the hair cells and these impulses are transferred to the brain via the vestibular nerve
glue ear: symptom
inflammation of the middle ear, muffled hearing and pus formation
glue ear: cause
infections by viruses and/or bacteria
glue ear: treatment
ear drops or a grommet for severe infections
smell
also called olfaction.
occurs in the nasal cavity.
there are specialised cells called olfactory receptor cells.
this group of cells senses the odours and sends signals to the brain via the olfactory bulb and olfactory nerve
taste
5 basic tastes: sweet, sour, salt, bitter & umami.
brain
composed of:
- cerebrum
- cerebellum
- medulla oblongata
- hypothalamus
- pituitary gland
cerebrum
- largest part
- composed of 2 symmetrical hemispheres.
- high folded surface giving extra area for neurons.
- divided into different lobes: frontal, temporal, parietal, occipital
frontal lobe
functions in reasoning, short-term memory, intelligence, personality, problem-solving, emotion & language.
temporal lobe
functions in long-term memory, speech & hearing
parietal lobe
functions in movement & touch
occipital lobe
functions in vision
cerebellum
- located at the back of the brain
- functions in control and coordination of movement.
medulla oblongata
- belongs to the brainstem (on top of the spinal cord).
- functions in breathing, heart rate, blood pressure, vomiting, coughing, sneezing & swallowing
hypothalamus
- small region of the brain located just above the brain stem and pituitary.
- functions in controlling the endocrine system via secretion of neurohormones such as growth hormone-releasing hormone (GHRH) and thyrotropin-releasing hormone (TRH).
- it also functions in controlling body temperature, hunger and thirst
pituitary gland
- the link between the nervous system and the endocrine system
- it releases many hormones including: growth hormone (GH) and thyroid-stimulating hormone (TSH).
parkinsons disease: cause
death of specific neurons deep within the brain.
the reasons for the death of these neurons is unknown but thought to be caused by exposure to pesticides.
parkinsons disease: symptoms
shaking and trembling of the hands, arms and legs during movement, a stiff and rigid body and fixed stare.
parkinsons disease: treatment
physiotherapy, exercise and a drug called levodopa
the spinal cord
- a bundle of nerve fibres enclosed within the spine, covered in specialised membranes called meninges and bathed in cerbrospinal fluid.
- it carries messages to and from the brain.
- it has 31 pairs of spinal nerves.
- there are structures called the dorsal root, dorsal root ganglion and a ventral root associated with each spinal nerve.
- the dorsal root carries sensory neurons
- the dorsal root ganglion contains the cell bodies of those sensory neurons.
- the ventral root carries the motor neurons.
- spinal cord is composed of white matter and grey matter. outer region = white. inner = grey.
- there is a central canal filled with cerebrospinal fluid.
reflex action
involuntary responses to a stimulus.
- carried out by reflex arcs.
- reflex arcs consist of a sensory neuron, an interneuron and a motor neuron.
- a common reflex action is the withdrawal reflex - touch something hot = pull hand away.
- the sensory neuron detects that something hot has been touched and sends a message to the spinal cord via the dorsal root.
- the sensory neuron synapses with an interneuron just inside the grey matter of the spinal cord and passes the message on.
- the interneuron relays the message onto the motor neuron, whose cell body is just inside the grey matter of the spinal cord.
- the motor neuron sends a message out through the ventral root to the skeletal muscles of the arm to pull the hand away from the hot object.
nervous system vs endocrine system: NERVOUS
speed of response: fast messages carried by: electrochemicals (ion movement) speed of transmission of message: fast length of response: short-lived areas affected: specific areas
nervous system vs endocrine system: ENDOCRINE
speed of response: slow messages carried by: chemical hormones speed of transmission of message: slow length of response: long-lived areas affected: wide areas
Ganglion
A group of cell bodies located outside the central nervous system
Threshold
The minimum stimulus needed to cause an impulse to be carried in a neuron
All or nothing law
States that if the threshold is reached an impulse is carried, but if the threshold is not reached no impulse is carried
Refractory period
A short time span after a neuron has carried an impulse during which a stimulus fails to cause a response
Synaptic cleft
A tiny gap between the two neurons at a synapse
Reflex arc
The pathway taken by a nerve Impulse in a reflex action
