Download The NERVOUS SYSTEM

THE NERVOUS SYSTEM
THE NERVOUS SYSTEM:
OVERVIEW
 Swift, brief response to stimuli
 Monitors internal & external environment
 Integrates sensory information
 Coordinates voluntary & involuntary responses of
other systems
ORGANIZATION
 Central Nervous System (CNS)
 Processes data and transmits commands
 Intelligence, memory, emotion
 Consists of:
 Brain
 Spinal cord
 Peripheral Nervous System (PNS)
 All neural tissue outside of the CNS
 “the highway” of communication
ORGANIZATION, CTD.
 PNS
 Afferent division
 Carries info from receptors to CNS
 Efferent division
 Carries commands from CNS to muscles, glands, adipose tissue in
body
 Divided into:
 Somatic Nervous System (SNS) – skel musc. contraxns
 Autonomic Nervous System (ANS) – automatic stuff like smooth &
cardiac muscle, glandular secretion, and adipose tissue…divided into:
 Sympathetic Nervous System
 Parasympathetic Nervous System
FIGURE 8.1
FIGURE 8.2
FIGURE 8.3
CELLULAR ORGANIZATION
 Neurons (carry electrical impulses)
 Cannot divide (lack centrioles)
 Neuroglia (supportive cells)
 Regulate environment
 Provide framework
 Phagocytic
 Smaller but more numerous
 Can divide
CLASSIFICATION OF NEURONS
Structural
 Pyrimidal Cell
found in brain
 Multipolar
 Motor neurons
 Unipolar
 Most sensory neurons
 Bipolar
 Some special sensory organs –
sight, smell, hearing
Functional
 Sensory neurons
 ~10 mil.
 Motor neurons
 ~500,000
 Interneurons
 ~20 billion!
SENSORY NEURONS
 Form afferent division of PNS
 Receive info from sensory receptors
 Monitor external and internal envts, then relay to CNS
 Somatic sensory receptors
 External receptors: touch, temp, pressure, sight, etc.
 Proprioceptors: monitor position and movement
 Visceral (internal) receptors
 Monitor digestion, respiration, CV, etc. and taste, deep pressure, and pain
MOTOR NEURONS
 Form efferent division of PNS
 Send messages to effectors (which DO
something)
 Somatic motor neurons (SNS)
 Visceral motor neurons (ANS)
INTERNEURONS
 Located in CNS only
 Connect other neurons
 Distribute info and coordinate activity
 Also play a role in planning, memory, and
learning
FIGURE 8.4
NEUROGLIA
 CNS Cell types:
 Astrocytes
 lg., numerous, maintain blood-brain barrier, repairs
 Oligodendrocytes
 Insulate axons (white matter/gray matter)
 Microglia
 small, rare phagocytes
 Ependymal
 line CNS cavities
NEUROGLIA
 PNS Cell types:
 Satellite cells
 Surround and support
neural cell
bodies
 Schwann cells
 Myelinate axons
CNS
 Demyelination
outside of
ANATOMICAL ORGANIZATION
 PNS
 Cell bodies (gray matter) located in ganglia
 Axons (white matter) bundled together into nerves
 CNS
 Collection of cell bodies with common function = center
 Center with discrete boundary = nucleus
 Neural Cortex: thick layer of gray matter
 Columns  made of tracts (bundles of axons of CNS)
 Pathways link centers to rest of body
MEMBRANE POTENTIAL
 All undisturbed cells are polarized
 Outside of cell has + charge, inside has –
 This is a potential difference, called membrane potential
 Unit = Volt (V) [cell membrane potential usu. measured in millivolts,
or mV
 “Normal,” or undisturbed cell’s membrane potential =
resting potential
 In neurons, resting potential is approximately -70mV
 Why is there a potential in resting cells?
FIGURE 8.7
WHAT HAPPENS WHEN IT CHANGES?
 Any substance that alters permeability of
membrane or alters the activity of pumps in the
membrane
 Exposure to chemicals
 Mechanical changes
 Temperature changes
 Change in extracellular fluid
 Change in resting potential can have an immediate
effect
VOCAB
 Depolarization
 Polarization
 Graded potential
 Ex: goblet/gland cell
 Action potential
 Skeletal muscles
 Axons of neurons
 Threshold
 Trigger analogy
 All – or – none principle
NEURAL COMMUNICATION
 Info travels thru action potentials (=electrical or nerve impulses)
 At end of axon, info (rls. of neurotransmitters) is passed to another neuron or to
an effector
THE CNS: ANATOMY
 Meninges

Provide physical stability and shock absorption

Three layers

Dura mater

Arachnoid


Cerebrospinal fluid
Pia mater
FIGURE 8.13
THE CNS:
ANATOMY
 The Spinal Cord

Cervical enlg.

Lumbar enlg.

Central canal


CSF
31 segments

Dorsal root (sensory) ganglia

Ventral root (motor)
FIGURE 8.15
THE CNS: ANATOMY
 The Brain
 6 Regions
 Cerebrum
 Conscious thought, sensation, intellectual fx, memory
storage and retrieval, complex movement
 Structure:
 Cortex – thick blanket of neural cortex
 Gyri/sulci or fissures– ridges/depressions
 Lobes – well defined regions
FIGURE 8.19
FIGURE 8.20
THE CNS: ANATOMY
 The Brain
 6 regions, ctd.
 Diencephalon
 Thalamus
 Hypothalamus (connected to pituitary gland)
 Emotions, autonomic fx, hormone production
 Epithalamus (pineal gland)
THE CNS: ANATOMY
 The Brain, ctd.

6 regions, ctd.

Midbrain



Pons

Connects cerebellum to brain stem

Tracts and relay centers, somatic and visceral motor control
Medulla oblongata


Visual, auditory, involuntary motor responses
Sensory info to thalamus and other centers, autonomic fx.
Cerebellum

Adjusts motor activities based on sensory information and stored memories of previous moments.
FIGURE 8.16
FIGURE 8.16C
CNS ANATOMY: THE VENTRICLES
 Ventricles

Chambers within the brain filled with CSF

Lateral: one in ea. cerebral hemisphere

Third ventricle: diencephalon

Fourth Ventricle: in pons and upper medulla oblongata (leads to central canal of spinal cord)
FIGURE 8.17
MEMORY
 Fact memories
 Skill memories
 Short-term memories (primary memories)

Don’t last long, but can be recalled immediately

Small bits of info

Repetition helps to ensure conversion to long-term
 Long-term memories

Last longer, sometimes a lifetime

Stored in cerebral cortex
 Memory consolidation = conversion
PNS: ANATOMY
 Peripheral Nerves

Cranial nerves

originate from the brain

12 pairs

Resp. for smell,
balance, muscle
and upper back…
info too
sight, hearing,
control over facial
provide sensory
FIGURE 8.25A
PNS: ANATOMY
 Peripheral Nerves, ctd

Spinal Nerves

Connect to the spinal cord

31 pairs, ea monitors a dermatome
FIGURE 8.27
REFLEXES
 Reflex arc

Wiring of a single reflex

Is this an example of positive or negative feedback?
 Types of reflexes

Monosynaptic – sensory neuron synapses directly on motor neuron

Ex: stretch reflex used by docs to test general condition of spinal cord, peripheral nerves, and
muscles.

Polysynaptic reflexes – contain interneurons, so longer delay between stimulus and
response

Withdrawal reflex

Flexor reflex
FIGURE 8.28
SENSORY PATHWAYS
FIGURE 8.31
FIGURE 8.32
THE AUTONOMIC NERVOUS SYSTEM
“In practical terms, conscious activities have little to do with our immediate or long
term survival…”
 Sympathetic

Fight or flight
 Parasympathetic

Rest and digest
FIGURE 8.33
AUTONOMIC NERVOUS SYSTEM
 The Sympathetic Nervous System

Stimulates tissue metabolism

Increases alertness

Prepares for emergency (sudden, intense activity)

Stimulates sweat glands and arrector pili muscles

Reduces circ. to skin and body wall

Accelerates blood flow to muscles

Releases stored lipids from fat tissue

Dilates pupils

Increases heart rate

Reduces blood flow by visceral organs not important to short term survival (digestion)
AUTONOMIC NERVOUS SYSTEM
 The Parasympathetic Nervous System

Constricts pupils

Increases secretions by digestive glands

Increases smooth muscle activity of digestive tract

Constricts respiratory pathways

Reduces heart rate

Relaxation, food processing, and energy absorption
FIGURE 8.34
AGING AND THE NERVOUS SYSTEM
 Reduction in brain size/weight
 Reduction in number of neurons
 Decreased blood flow to brain
 Fewer dendritic branchings and interconnections, neurotransmitter production goes
down
 Intracellular and extracellular changes in neurons
 Memory consolidation more difficult
 Senses less acute
 Reaction times and reflexes slower
 Precision of motor control decreases