Transcript The Nervous System

Senses and Perception
Lab 17
Organization of the Vertebrate
Nervous System

Central nervous system (CNS) –
brain & spinal cord.


Responsible for more complex reflexes
and higher associative functions like
learning & memory.
Peripheral nervous system
(PNS) – motor and sensory
neurons.
Organization of the Vertebrate
Nervous System


Motor neurons
carry impulses
away from the
CNS to effectors
(muscles and
glands).
Sensory neurons
carry impulses
from sensory
receptors to the
CNS.
Reflexes

A reflex produces
a very fast motor
response to a
stimulus because
the sensory
neuron bringing
information about
the threat passes
the information
directly to the
motor neuron.
Sensory Receptors

The sensory nervous system
carries impulses to the CNS.


Sensory receptors are specialized
sensory cells that detect changes in
blood pressure, strain on ligaments,
and smells in the air, among other
things.
Complex sensory receptors made of
many cell & tissue types are called
sensory organs.

Eyes, ears, taste buds.
Sensory Receptors

The brain can tell what kind of
impulse is coming (light, sound,
pain, etc) because the signal came
from a particular type of receptor.

Light signals come from light receptors.
The Path of Sensory Information

There are many different kinds of
sensory receptors.


Exteroceptors are receptors that
sense stimuli that come from the
external environment.
Interoceptors sense stimuli that come
from inside the body.
Sensing Chemicals: Taste

Taste – taste buds
embedded in the
surface of the tongue
contain taste receptor
cells.


Chemicals from food
dissolve in saliva and
contact the taste cells.
Salty, sour, sweet, &
bitter chemicals are
detected in different
ways.
Sensing Chemicals: Smell

Smell – chemically sensitive neurons in
the nose detect chemicals and transmit
the information to the brain where smell
information is processed & analyzed.
Sensing Sounds: Hearing

Hearing a sound involves detecting
the vibrations of the air.


Waves of pressure in the air beat
against the ear push the eardrum in &
out.
Three small bones on the other side of
the eardrum increase the force of the
vibration.
Sensing Sounds: Hearing


The vibration
crosses a second
membrane to the
fluid of the inner
ear – the cochlea.
The inner ear is
connected to the
throat by the
eustachian tube
to equalize
pressure.
Sensing Sounds: Hearing


The sound receptors occur in the
cochlea.
When sound vibrations enter the
cochlea, they send nerve impulses
to the sensory neurons that travel
to the brain.
Sensing Sounds: Hearing


Sounds of different frequencies
cause different parts of the
membrane inside the cochlea to
vibrate and fire different neurons.
Intensity is determined by how
often the neurons fire.
Sensing Light: Vision


Vision is the perception of light.
The eye is a special sensory organ
that uses pigments in structures
called rods and cones to absorb
photons of light.
Structure of the Vertebrate Eye


Light passes through
the transparent
cornea which begins
to focus light on the
rear of the eye, then
through the lens
which completes the
focusing.
The lens is
suspended by ciliary
muscles.
Structure of the Vertebrate Eye


The iris is a shutter that controls
the amount of light entering the
eye.
The pupil is the transparent zone in
the center of the iris that gets
larger in dim light and smaller in
bright light.
Structure of the Vertebrate Eye


The light is focused by the lens onto
the back of the eye.
An array of light sensitive receptor
cells called the retina line the back
of the eye.

Rods & cones – two types of receptor
cells generate nerve impulses that pass
along the optic nerve.
Structure of the Vertebrate Eye


Rods are very
sensitive to light
and can detect
shades of gray in
very dim light, but
they do not detect
color and the
images are not
sharp.
Cones detect
colors and produce
sharp images.
Color Vision



Three kinds of cone
cells allow color
vision.
Each has a different
version of the opsin
protein and so
absorbs different
wavelengths of light.
The brain compares
relative intensities of
the signals from the
three types of
cones.
Binocular Vision



Primates and most predators have two
eyes facing forward, so the field of view
overlaps.
This binocular vision allows perception
of 3D images and depth.
Animals with eyes on the sides can detect
motion in a wider field – good for prey
animals.