Subdivisions of Nervous System
Subdivisions of Nervous System
Gray and White Matter
•
•
Gray matter = neuron cell bodies,
dendrites, and synapses
– forms cortex over cerebrum
and cerebellum and central
portion of spinal cord.
– forms nuclei deep within brain
White matter = bundles of axons
– forms tracts that connect parts
of brain.
– Ascending and descending
tracts in the spinal cord.
Fiber Tracts in White Matter
• White Matter: Fibers and
tracts that allow for
communication to/from and
between the various cortical
areas
– Commissures – connect
corresponding gray areas of
the two hemispheres
• (Corpus Collusum)
– Projection fibers – enter the
hemispheres from lower brain
or cord centers
• Sensory neurons project up to
the cortex.
• Motor descend away from the
cortex.
Fiber Tracts in White Matter
– Association fibers – connect different parts of the same
hemisphere.
– I.e. You see a tiger on the loose. You get and get scared
because visual association fibers project to many areas of the
brain including the limbic system and motor system.
Meninges
• Dura mater: outermost,
tough membrane
– outer periosteal layer
against bone
– where separated from inner
meningeal layer forms
dural venous sinuses
draining blood from brain
• Arachnoid layer:
– subarachnoid space were
cerebral spinal fluid flows
• pia mater:
– is thin layer in direct
contact with brain tissue
Functional Areas of the Cerebral
Cortex
• The three types of functional areas are:
– Motor areas – control voluntary movements.
• Innervates striated muscle
– Sensory areas – conscious awareness of
sensation
• Receives sensory (afferent input from the eyes,
ears , skin, muscles and joints)
– Association areas – integrate various areas of
the brain.
• They give context and meaning to various sensory
input based on previous experience.
Cerebral Cortex
• The cortex – superficial gray matter; accounts
for 40% of the mass of the brain
• It enables sensation, communication, memory,
understanding, and voluntary movements
• Each hemisphere acts contralaterally (controls
the opposite side of the body)
• No functional area acts alone; conscious
behavior involves the entire cortex
Functions of Cerebrum - Lobes
• Frontal
– voluntary motor functions
– planning, mood, smell and social judgement
• Parietal
– receives and integrates sensory information
• Occipital
– visual center of brain
• Temporal
– areas for hearing, smell, learning, memory,
emotional behavior
Functional Regions of Cerebral Cortex
Primary Motor Cortex
Located on precentral gyrus. Initiates motor responses that
control voluntary muscles of speech and movement. The
entire body is mapped here. Considered the pyramidal
motor system.
Motor Control
• Precentral gyrus
(primary motor area)
relays signals to spinal
cord to supply muscles
of opposite side
• Motor homunculus proportional to number
of muscle motor units in
a region
– Greater # of motor units
allows for fine movement
patterns.
• Face, mouth, hands, feet
Supplemental Motor/Pre Motor Cortex
Located just anterior to precentral gyrus. Involved with controlling and planning
learned movement responses. SMC controls sequence of movements from
memory .Supplemental motor cortex driven by intention while pre motor
cortex appears to be driven to movements guided by a visual cues. May
effect the primary motor cortex directly or directly contribute to the cortical
spinal tract.(15%)
Prefrontal Cortex
• The highest developed part of the brain. Involved in
higher thought processes such as judgment, working
memory, personality, abstract thinking.
• Closely linked to the limbic system (emotions)
• Movement requires the input from many
cortical areas.
Sensory Perception
• Specific receptors for touch, pressure, stretch,
temperature, and pain transmit afferent impulses
from the external environment to the cortex
• Somatosensory area in postcentral gyrus
Sensory Homunculus
• Area of cortex dedicated to sensations of body parts is proportional
to the sensitivity of that body part (# of receptors)
– The face mouth ,hands and feet have the greatest amount of receptors
which allows the greatest discrimination of touch.
Speech Areas
• Wernicke’s Area: Sensory in
nature
• involved in speech
comprehension
– Damage results in receptive
aphasia
• Broca’s Area: involved in
speech production.
• Coordinates respiratory and
oral movements
– Damage results in expressive
aphasia
Functions of the limbic system: learning emotion appetite (visceral
function),sex and endocrine integration.
Key structures include:
1. Hippocampus: learning and memory
2. Amygdala: processing emotions such as fear. (emotional memory)
3. Hypothalmus: regulate autonomic endocrine and visceral functions.
4. Ventral Tegmental Area: (VTA) Area in midbrain containing nuclei that
have dopamine containing neurons involved endogenous reward
center.
Reticular Formation of Midbrain
• Midbrain
– Reticular Formation
regulates sleep,
wakefulness and
arousal
• Reflex Orientation to
sensory stimulus
– Visual
• Superior colliculi
– Auditory
• inferior colliculi
Cerebellum
• Cerebellum
– Compares descending
cortical input to ascending
proprioceptive (sensory)
input and figure out the
most efficient way to move.
– Critical for the timing of
learned skilled motor
programs
– It can make online changes
to motor programs on the
– Helps us maintain muscle
tone, posture, and smooth
muscle contractions
• Distinguish pitch and similar
sounding words
Anatomy of the Spinal Cord
• Cylinder of nerve tissue within the vertebral
canal (thick as a finger)
– vertebral column grows faster so in an adult the
spinal cord only extends to L1-2
• 31 pairs of spinal nerves
– 8 cervical (C1-C8)
– 12 thoracic (T1-T12)
– 5 Lumbar (L1-L5)
– 5 Sacral (S1-S5)
– 1 Coccygeal (C0)
Functions of the Spinal Cord
• Conduction
– bundles of fibers passing information up and down spinal
cord
• Locomotion
– repetitive, coordinated actions of several muscle groups
– central pattern generators are pools of neurons providing
control of flexors and extensors (walking)
• Reflexes
– involuntary, stereotyped responses to stimuli (remove
hand from hot stove)
– involves brain, spinal cord and peripheral nerves
Meninges of Vertebra and Spinal
Cord
Cross-Sectional Anatomy of the Spinal
Cord
• Central area of gray matter shaped like a butterfly and
surrounded by white matter in 3 columns
• Gray matter = neuron cell bodies with little myelin
• White matter = myelinated axons
Gross Anatomy of Lower Spinal Cord
• The amount of white
matter relative to grey
matter decreases as you
move down the cord.
– Cervical :lots of white
matter, ventral horn
enlargements.
– Thoracic: small dorsal and
ventral horns.
Intermediate horn for the
sympathetics in the body,
– Lumbar: Round cord,
ventral horn enlargements
– Sacral: Small round cord,
almost no white matter.
Peripheral Nerves
• Consist of 31 pairs of
spinal nerves and 12
cranial nerves.
• They extend from
both the brain and
spinal cord to their
effecter organ.
• ganglion = groups of
cell bodies in a nerve
that are located outside
the (CNS)
Anatomy of a Nerve
• A nerve is a bundle of nerve fibers (axons)
• Epineurium covers nerves, perineurium surrounds a
fascicle and endoneurium separates individual nerve
fibers
Anatomy of Ganglia in the PNS
• Cluster of neuron cell bodies in nerve in PNS is the
dorsal root ganglion
Functional Divisions of PNS
• Sensory (afferent) divisions (receptors to CNS)
– visceral sensory( messages from organs) allow our
CNS to interpret internal environments.
– somatic sensory division ( messages from skin, joints,
muscles) allow our CNS to interpret both our external
environments.
• Motor (efferent) division (CNS to effectors) response to the
environment through excitation of:
– visceral motor division (ANS) Involuntary
effectors: cardiac, smooth muscle, glands
• sympathetic division (fight or flight)
• parasympathetic division (rest and digestion)
– somatic motor division (voluntary)
effectors: skeletal muscle
Cranial Nerves
• 12 pairs of cranial nerves originate from the base of the brain
• They control a variety of functions relating to the head, neck, and
internal organs
• Why do we care about their functions and what does it mean if there are
deficits in one or more cranial nerves?
Autonomic Nervous System
• Motor nervous system controls glands, cardiac
and smooth muscle
– also called visceral motor system
• Regulates unconscious processes that
maintain homeostasis
– BP, body temperature, respiratory airflow
• ANS actions are automatic
– biofeedback techniques
• train people to control hypertension, stress and migraine
headaches
Divisions of ANS
•
Two divisions innervate same target organs
–
may have cooperative or contrasting effects
1. Sympathetic division ( Fight and Flight)
–
prepares body for physical activity or any kind of stress!
•
increases heart rate, BP, airflow to organs vital for dealing with
the stress( skeletal muscles, heart brain), blood glucose levels to
ensure you have enough fuel to get out of trouble, etc
–
If you are chased by a tiger he won’t be very sympathetic
2. Parasympathetic division (Rest and Digest)
–
calms many body functions and assists in rest and
restoration functions such as digestion and waste
elimination.
•
Decreased heart rate, BP and blood will be shunted away from
skeletal muscles and towards vital organs i.e. intestinal tract.
Somatic Nervous vs. Autonomic Nervous
Division
• Motor pathways of the somatic division consist of a
single motor neuron that extends from the spinal cord
to skeletal muscle.
• Motor pathways of the ANS consist of a two neurons
between the brain or spinal cord and the effector
– the preganglionic begins in the brain or spinal cord
and extends to a ganglion (soma of postganglionic
neuron)
– the postganglionic neuron which extends from the
ganglion to an effector organ
Motor Pathways of the Somatic Nervous Division
vs. Autonomic Nervous Division
Efferent Sympathetic vs. Parasympathetic
Ganglia and Abdominal Aortic Plexus
Adrenal Glands
• Paired glands sit on superior pole of each kidney
• Cortex (outer layer)
– secretes Aldosterone, Cortisol, gonadocorticoids
• Medulla (inner core)
– a modified sympathetic ganglion
• stimulated by preganglionic sympathetic neurons
– secretes neurotransmitters (hormones) into blood
• catecholamines (85% epinephrine and 15%
norepinephrine)
• The result is:
– an increase in blood glucose levels via glycogenolysis
and gluconeogenesis in the liver
– the vasoconstriction of blood vessels and redirecting
blood flow toward the brain, heart and skeletal
muscles.
– Increase in heart rate and stroke volume
Sympathetic and Vasomotor Tone
Fight and Flight:
Sympathetic division
prioritizes blood vessels to
skeletal muscles and heart
in times of emergency.
Blood will be shunted
away from digestive tract.
During times of resting or
digesting vasoconstriction
of vessels to the skeletal
muscles and dilatation of
the vessels of the
digestive tract.
Dual Innervations of the Iris
• ANS has membrane receptors to
both ACh and NE
• Depending on which
neurotransmitter is released
– PNS releases of ACH from its
postganglionic neuron which
will cause the pupils to
constrict.
– The SNS causes the release of
NE from the postganglionic
neuron. That will bind to its
receptor causing the opposite
( pupils dilate)
• The heart :
– NE increases both force and
rate of heart contraction
– ACh decreases both force and
rate heart contraction.