Biology: Nervous System Flashcards
What makes up the CNS?
Brain and spinal cord
How many spinal nerves?
31 pairs - fan out from the spinal cord to form the PNS
What is the nerve impulse path?
sensory receptor stimualted
nerve impulse sent via a sensory neurone of the PNS to CNS
then away from CNS via a motor neurone to an effector
What is the reflex arc?
sensory receptor neurones stimulated
nerve impulse sent via an afferent neurone to a motor neurone via interneurone in the spinal cord
What can override the reflex arc?
cerebral cortex
What does the ANS do ?
controls the autonomic functions of the body that maintain stable internal conditions (respiration, HR, BP, temperature and salt-water balance)
What does the hypothalamus do ?
regulates many of the body’s autonomic systems (vasodilation/vasoconstriction)
What does the iris do ?
controls the amount of light entering the pupil by contracting the circular muscle (for bright light) or the radial muscle (in dim light)
What does the autonomic reflex arc do ?
it causes dilation or constriction of the pupil
Where are photoreceptors located?
light sensitive rod and cone cells present in the retina
What do photoreceptors do ?
measure intensity, wavelength and position of light
What happens to impulses after reaching the photoreceptors?
impulses are relayed via the ganglion cells to the optic nerve which transmits impulses to the brain
What happens to the image on the retina?
the image is inverted and results from the refraction of light at the cornea with fine adjustment at the lens
Where is the image sharpest?
sharpest near the centre of the retina at the fovea
What does the accommodation reflex do ?
it changes the focus of the lens from infinity (parallel light) to a near object
- focus at a near object= maximum accommodation= maximum curvature - more spherical
