Download SBI 4U Homeostasis 3

Homeostasis 3:
The Central Nervous System
And
The Peripheral Nervous System
What’s the Matter?
Grey Matter: is grey because it contains
mainly unmyelinated axons, cell bodies,
dendrites. It is found around the
outside areas of the brain and forms the
H-shaped core of the spinal cord.
White matter: contains myelinated
axons that run together in tracts.
Forms the inner region of the brain and
outer region of the spinal cord.
The Spinal Cord
Vital communication link between the brain
and the peripheral nervous system.
Sensory nerves carry messages from the
body to the brain for interpretation
Motor nerves relay messages from the
brain to the effectors.
The spinal cord has a ventral side and a
dorsal side, white matter and grey matter.
The tissues are protected by cerebrospinal
fluid, soft tissue layers and the spinal
column.
The Brain
The brain can be subdivided into
three general regions: the
hindbrain, midbrain and forebrain.
The skull protects the brain as well
as the meninges.
Three layers of tough, elastic tissue
within the skull and spinal column.
Hindbrain
 Controls coordination and
homeostasis
 Cerebellum: involved in
unconscious coordination of posture,
reflexes, body movements as well as
fine voluntary motor skills and
receives info from proprioceptors in
muscles and joints.
 Medulla Oblongata:coordinates
many reflexes and automatic body
functions such as heart rate, blood
vessel size, rate of breathing,
swallowing and coughing.
 Pons: relay centre between right
and left halves of brain.
Midbrain
 Processes sensory
input.
 The Midbrain takes
in information from
the eyes, ears and
nose and relays info
between areas of the
hindbrain and
forebrain
 Controls eye
movement and
skeletal muscles.
The Forebrain
 Thalamus: provides connections
from different parts of the brain,
acts as a relay station between
forebrain and hindbrain, sensory
and cerebellum
 Hypothalamus: regulates
body’s internal environment and
some aspects of behaviour.
Controls blood pressure, heart
rate, body temp, thirst, hunger,
emotions. Also links the nervous
and endocrine systems
 Cerebrum: largest part.
Contains centres for intellect,
learning, memory,
consciousness, language.
The Blood-Brain Barrier
The meninges protect the CNS by preventing
direct circulation of blood through the cells of
the brain and spinal cord.
Blood supply to the brain are made up of
tightly fused epithelial cells and large amounts
of glial cells called astrocytes surround the
capillaries.
Oxygen and glucose can pass through easily.
Other lipid-soluble substances such as caffeine,
nicotine and alcohol can pass through to the
brain directly as well, which explains their rapid
effects on brain function.
This protects the brain from toxins and
infectious agents.
Cerebrospinal Fluid
Within the spaces of the brain and
spinal column is a fluid called the
cerebrospinal fluid.
It moves hormones, white blood cells,
and nutrients across the blood-brain
barrier.
Cerebrospinal fluid also acts as a
cushion to the brain as it circulates
between two layers of the meninges,
the arachnoid and pia mater.
The Cerebrum
The cerebral cortex is responsible for language,
memory, personality, vision, conscious thought
and more.
It is folded in order to increase surface area.
The right and left halves are known as the
hemispheres and are joined by a bundle of
white matter called the corpus collosum.
In general the right-brain is associated with
holistic and intuitive thinking, visual-spatial
skills, and artistic abilities. The left-brain is
linked to segmental, sequential, and logical
ways of thinking and to linguistic and
mathematical skills.
The Cerebral Cortex
Can be divided into four pairs of lobes.
Occipital Lobe: receives and analyses
visual information.
Temporal Lobe: help with the
processing of visual information, but
mainly their function is auditory
reception. Linked to understanding
speech and retrieving visual and verbal
memories
Parietal Lobe: receive and process
sensory information from the skin.
Help to process information on the
body’s position and orientation.
Frontal Lobe: named for their location
at the front of the cerebrum. Integrate
info from other parts of the brain and
control reasoning, critical thinking,
memory and personality. Contains
motor areas for precise voluntary
movements. The nerves leading from
the left and right frontal lobes cross
over in the brainstem, so that each side
of the brain actually controls muscles
on the opposite side of the body.
The Peripheral Nervous System
Consist of nerves that link the brain and
spinal cord with the rest of the body,
including senses, muscles, glands and
internal organs.
Sensory neurons carry information to
the CNS
Motor neurons carry information from
the CNS to the effectors.
There are two main divisions in the
PNS: somatic and autonomic.
Somatic System
Voluntary control
Includes 12 pairs of
cranial nerves, 31
pairs of spinal
nerves
Carry information
about the external
environment
through sensory
nerves to the CNS.
The Autonomic System
Involuntary control
Nerves stimulate or inhibit glands,
cardiac muscle and smooth muscle.
Maintains homeostasis
Hypothalamus and medulla oblongata
control the autonomic nervous system,
which has neurons that are bundled
together with somatic system neurons
in the cranial and spinal nerves.
Has two divisions: sympathetic and
parasympathetic.
Sympathetic Nervous System
Typically activated in stressful
situations. Often referred to as the
fight-or-flight response
Sympathetic neurons release
norepinephrine that has an excitatory
affect on its target muscles.
Sympathetic nerves trigger the adrenal
glands to release epinephrine that
further activates the stress response.
Blood pressure increases, heart rate
increases.
Parasympathetic Nervous
System
Activated when body is calm and at rest.
Restores and conserves energy
Slows heart rate, lowers blood pressure,
promotes food digestion
Uses acetylcholine to control organ responses.
Certain drugs can directly affect the
sympathetic and parasympathetic systems. i.e.
caffeine stimulates the sympathetic nervous
system to increase the heart rate and blood
pressure.
Practice:
Page 369 #1-16
Page 373 #1-5, 11.