sensory neurone
motor neurone
spinal cord
muscle (effector)
pain receptors
B10) THE HUMAN NERVOUS SYSTEM
Information from receptors passes along cells (neurones) as electrical impulses to the central nervous system (CNS) | |
The CNS is the brain and the spinal cord. | |
Coordinates the response of effectors; muscles contracting or glands secreting hormones | |
Stimulus | Lights switch on |
Receptor | Cells in retina |
Coordinator | CNS |
Effector | Muscles connected to iris |
Response | Pupils get smaller |
Human control systems include | Cells called receptors | Detect stimuli (changes in environment). |
Coordination centres | e.g. brain, spinal cord and pancreas that receive information from receptors. | |
Effectors | Muscles or glands, which bring about responses to restore optimum levels. |
The human nervous system
Enables humans to react to their surroundings and to co-ordinate their behaviour
Synaptic cleft
vesicles
axon terminal
axon
neurotransmitter
neurotransmitter
receptors
direction of impulse
dendrites
cell body
nucleus
axon with insulating sheath
axon terminal
Reflex arc | Receptor | Detect stimuli. |
Sensory neurone | Long axon carries impulse from receptor to spinal cord. | |
Synapse | Gap where neurones meet. Chemical message using neurotransmitter. | |
Relay neurone | Allows impulses to travel between sensory and motor neurones in the spinal cord. | |
Motor neurone | Long axon carries impulse from receptor to effector. | |
Effector | Muscle or gland that carries out response. |
Reflex actions are automatic and rapid; they do not involve the conscious part of the brain and can protect humans from harm.
Typical motor neurone
Synapse (gap where two neurones meet).
The brain controls complex behaviour. It is made of billions of interconnected neurones.
The Brain
(Bio only)
The brain has different regions that carry out different functions. | Cerebral cortex | Largest part of the human brain. Higher thinking skills e.g. speech, decision making. |
Cerebellum | Balance and voluntary muscle function e.g. walking, lifting. | |
Medulla | Involuntary (automatic) body functions e.g. breathing, heart rate. |
medulla
cerebellum
cerebral cortex
(HT) The complexity and delicacy of the brain makes investigating and treating brain disorders very difficult
Treating brain damage and disease | e.g. Lobotomy – cutting part of the cerebral cortex | Benefit: thought to alleviate the symptoms of some mental illnesses. |
Risks: bleeding in the brain, seizures, loss of brain function. Procedure was abandoned in the 1950s due to risk. |
Neuroscientists have been able to map regions of the brain by studying patients with brain damage, electrical stimulation and MRI.
The Eye (Bio only)
retina
optic nerve
sclera
cornea
iris
ciliary muscles
suspensory ligament
Sense organ containing receptors sensitive to light intensity and colour
Structures of the eye | Retina | Light sensitive cell layer. |
Optic nerve | Carries impulse to brain. | |
Sclera | Protects the eye. | |
Cornea | Transparent layer that covers the pupil and iris. | |
Iris | Pigmented layer, controls size of pupil. | |
Ciliary muscles | Controls thickness of lens. | |
Suspensory ligaments | Connects lens to ciliary muscles. |
The iris can dilate the pupil (aperture) to let in more light in dim conditions
Accommodation is the process of changing the shape of the lens to focus | |
Near object | Far object |
Ciliary muscles contract, suspensory ligaments loosed, lens get thicker, light is more refracted. | Ciliary muscles relax, suspensory ligaments pulled tight, lens pulled thin, light is only slightly refracted. |
New technologies now include hard/soft contact lens, laser surgery to change the shape of the cornea and a replacement lens in the eye.
Hyperopia (long sightedness) | Myopia (short sightedness) |
Treated using a convex lens so the light is focused on the retina. | Treated using a concave lens so light is focused on the retina. |