Download Chapter 39 Neural Signaling and Chapter 40 Neural Regulation

Chapter 39 Neural Signaling and
Chapter 40 Neural Regulation
The Nervous System
Parts of a Neuron
• Receive stimuli
• Produce and transmit electrical signals ( aka
nerve impulses/action potentials)
• Synthesize and release neurotransmitters
• Draw neuron
• Many axons make nerve
• Tracts/pathways – bundles of axons in CNS
• Ganglia – groups of cell bodies outside CNS
• Nuclei – groups of cell bodies inside CNS
Fig. 48-12
Node of Ranvier
Layers of myelin
Axon
Schwann
cell
Axon
Nodes of
Myelin sheath Ranvier
Schwann
cell
Nucleus of
Schwann cell
0.1 µm
Neural Signaling: 4 processes
(communication among neurons)
• Reception
– Detect a stimulus
– Neurons and sense organs
• Transmission
– Message sent along neuron, between neurons, to
effector
• Integration
– Sort and interpret incoming info, determine response
• Action by effectors
– Actual response to stimulus
Fig. 48-3
Sensory input
Integration
Sensor
Motor output
Effector
Peripheral nervous
system (PNS)
Central nervous
system (CNS)
Types of Neurons
• Sensory neurons aka Afferent neurons
– Info TO CNS
• Interneurons aka Association neurons
– Info from afferent neurons to interneurons
– Integrate and output
– Most common
– Cell body and axon in CNS
• Motor neurons aka Efferent neurons
– Carries message from CNS to effector
Glial Cells (neuroglia)– support and protect neurons,
regulatory functions - CNS
• Microglia
– Phagocytes – remove debris
• Astrocytes
– Star-shaped
– Provide glucose to neurons
– Regulate extracellular fluid
• Oligodendrocytes
– Form sheath of myelin around neurons
• Schwann cells
– Outside of CNS
– Form sheaths around some axons
Fig. 49-6
PNS
CNS
VENTRICLE
Neuron
Astrocyte
Ependymal
cell
Oligodendrocyte
Schwann cells
Microglial
cell
Capillary
50 µm
(a) Glia in vertebrates
(b) Astrocytes (LM)
• Nerve impulse
• Myelin
• Multiple sclerosis
Synapses
• Presynaptic neuron / Postsynaptic neuron
• Electrical synapse
• Chemical synapse
Electrical synapse
• 2 neurons very close together
• Interiors of 2 cells physically connected by
protein channel
• Ion passage between cells, permitting an
impulse to be directly and rapidly transmitted
from pre to postsynaptic neuron
• Used for escape responses
Chemical synapse
• More common
• 2 neurons separated by synaptic cleft
• Depolarization of property of PM so when
action potential reaches end of axon it is
unable to jump the gap
• Electrical signal must be converted to
chemical signal (neurotransmitter)
• When postsynaptic neuron reaches threshold
depolarization, it transmits an action potential
Fig. 48-15
5
Synaptic vesicles
containing
neurotransmitter
Voltage-gated
Ca2+ channel
Postsynaptic
membrane
1 Ca2+
4
2
Synaptic
cleft
Presynaptic
membrane
3
Ligand-gated
ion channels
6
K+
Na+
• Neurotransmitter – conduct neural signal across
synapse and bind to chemically activated ion
channels in PM of postsynaptic neuron
– Ex: acetycholine
– Norepinephrine, serotonin, dopamine
• Neuromodulator – messengers that modify the
effects of specific neurotransmitters
– Some amplify/dampen response by postsynaptic cell
How Neurotransmitters (NT) work
•
•
•
•
Stored in synaptic terminals in synaptic vesicles
Action potential reaches synaptic terminal
Voltage-gated calcium channels open
Calcium ions from extracellular fluid flow into
synaptic terminal
• Ca ions cause synaptic vesicles to fuse with
presynaptic membrane and release NT into synaptic
cleft by exocytosis
• NT diffuse across synaptic cleft and combine with
specific receptors on dendrites or cell bodies of
postsynaptic neurons (or PM of effector cells)
• Ligand-gated ion channel – NT receptor,
chemically activated
• Ligand (NT) binds with receptor and ion
channel opens
• Ex: Ach receptor is ion channel for passage of
Na+ and K+
Resting Potential Video
Action Potential Video
Synapse Video
Repolarization - Quick
• Excess NT must be removed
• Degraded by enzymes
– Ex: Acetylcholinesterase breaks Ach  choline +
acetate
• Active transport back into synaptic terminal =
reuptake
– Repackaged and recycled
Drugs inhibit reuptake
• Antidepressants
• SSRIs – selective serotonin reuptake inhibitors
– Fluoxetine (Prozac)
• Cocaine - dopamine
NT – different effects with different
neurons
• Ach
– Excite – skeletal muscle
– Inhibit – cardiac muscle
• Excitatory postsynaptic potential (EPSP)
– Change in membrane potential that brings neuron
closer to firing
• Inhibitory postsynaptic potential (IPSP)
– Change in membrane potential that takes the
neuron farther away from firing
How Neurons Work
Video
Chapter 40: Neural Regulation
• Vertebrate Nervous System
• CNS
– Complex brain continuous with spinal cord
– Central control
– Integrate incoming info
– Determine appropriate response
• PNS
– Sensory receptors and nerves (communication
lines)
Fig. 49-4
Central nervous
system (CNS)
Brain
Spinal
cord
Peripheral nervous
system (PNS)
Cranial
nerves
Ganglia
outside
CNS
Spinal
nerves
Fig. 49-5
Gray matter
White
matter
Ventricles
• Cranial nerves
– Link body parts to brain
• Spinal nerves
– Link body parts to spinal cord
Vertebrate Brain
• Brainstem = medulla, pons, midbrain
– Medulla
• Most posterior
• Regulate respiration, heartbeat, BP, swallowing,
coughing, vomiting
– Pons
• Mammals
• Bulge anterior of brain stem
• Bridge – connects spinal cord and medulla with upper
parts of brain
• Regular respiration
• Relay impulses from cerebrum  cerebellum
Fig. 49-UN1
– midbrain
•
•
•
•
(mesencephalon)
Visual reflexes (pupil constriction)
Auditory reflexes
Muscle tone and posture
• Cerebellum
– Muscle activity – tone, posture, equilibrium
(balance)
• Thalamus
– Relay center for motor and sensory messages
• Hypothalamus
– Below thalamus
– Olfactory centers
– Principal integration center for regulation of
viscera
– Provides input to medulla and spinal cord that
regulate heart rate, respiration, digestive function
– Controls body temp.
– Regulates appetite, water balance
– Emotional/sexual responses
– Links nervous and endocrine systems, produces
certain hormones
• Cerebrum
– Most prominent
– Olfactory
– R and L hemispheres
– Mostly white matter (mainly myelinated axons
that connect various parts of brain)
– Surface  convolutions = numerous folds
• Expands surface
• Sulci – furrows between convolutions if shallow
• Fissures if deep
– # folds associated with complexity of brain
function
– Gray matter – cerebral cortex
• Makes up outer portion of cerebrum
• Contains cell bodies and dendrites
Human CNS
• Well-protected brain and spinal cord
• 3 layers connective tissue (meninges) and
encased in bone
• 3 meningeal layers
– Outer dura mater
– Middle arachnoid
– Thin vascular pia mater (adheres closely to tissue
of brain and spinal cord)
• Meningitis – disease where these coverings
become infected and inflamed
• Cerebrospinal fluid (CSF)
– Between arachnoid and pia mater, in subarachnoid space
– Produced by choroid plexus = special networks of
capillaries extend up from pia mater into brain ventricles;
extract nutrients from blood and adds them to CSF
– Choroid plexus and arachnoid serve as barrier between
blood and CSF (prevent harmful substances from entering
the brain)
• CSF
– Shock absorber
– Cushions brain and spinal cord
– Medium for exchange of nutrients and waste
products between brain and blood
Spinal Cord
• Base of brain to L2 vertebra
• Central canal surrounded by gray matter (cell
bodies, dendrites, unmyelinated axons, glial
cells) in “H” shape
• White matter (outside gray matter) of
myelinated axons in bundles (tracts)
Reflex action
• Relatively fixed response pattern to a simple
stimulus
• Predictable, automatic, unconscious
• Ex: breathing
Withdrawal reflex
• Touch hot stove, jerk hand away
• Route of the message
– Pain receptor in skin  sensory neuron  spinal
cord  association neuron  appropriate motor
neuron  group of muscles
• Same time – message sent to conscious areas
of brain (up spinal cord)
– Aware, feel pain (not part of reflex)
Fig. 49-3
Quadriceps
muscle
Cell body of
sensory neuron in
dorsal root
ganglion
Gray
matter
White
matter
Hamstring
muscle
Spinal cord
(cross section)
Sensory neuron
Motor neuron
Interneuron
Human Cerebrum
• Cerebral cortex (outer part of cerebrum)
• R and L cerebral hemispheres
• Functionally divided into 3 area
– 1 – sensory – receive incoming signal from sense
organs
– 2 – motor – control voluntary movement
– 3 – association – link sensory and motor areas,
responsible for thought, learning, language,
memory, judgment, personality
• Occipital lobes – vision
• Temporal lobes – hearing
• Central sulcus – groove across top of each
hemisphere from medial to lateral edge
– Partially separate frontal lobes from parietal lobes
• frontal lobes – skeletal muscles
• Parietal lobes – heat, cold, touch, pressure
from skin
Fig. 49-15
Frontal lobe
Parietal lobe
Speech
Frontal
association
area
Somatosensory
association
area
Taste
Reading
Speech
Hearing
Smell
Auditory
association
area
Visual
association
area
Vision
Temporal lobe
Occipital lobe
• Size of motor area in brain for a given body
part proportional to complexity of movement
involved
– Ex: hands and face = large areas
• One side of brain controls opposite side of
body
• Uppermost part of cortex controls lower limbs
of body
• White matter of cerebrum under cerebral
cortex
• Nerve fibers of white matter connect the
cortical areas with 1 another and with other
parts of the nervous system
• Corpus callosum - Large band of white matter,
connects R and L hemispheres
• Basal ganglia
– Deep in white matter
– Paired groups of nuclei (gray matter)
– Coordination and movement
– Send signals to midbrain
• Cerebral cortex – integrates info about diverse
activities
– Arousal, sleep, emotion, information processing
The Brain and Sleep-wake
• “brain waves” / electrical potentials generated
by active neurons can be measured
• Recorded by electroencephalogram (EEG)
• Electrodes taped to scalp and activity of
cerebral cortex measured
• Alpha waves
– Most regular indication of activity
– Occur rhythmically ~ 10/sec.
– Mostly from visual areas in occipital lobe (rest
quietly, eyes closed)
• Beta waves
– Rapid, irregular waves, eyes open
– Fast frequency
– Heightened mental activity
• Delta and theta waves
– Slow, large waves associated with certain stages of
sleep
Fig. 49-11
Key
Low-frequency waves characteristic of sleep
High-frequency waves characteristic of wakefulness
Location
Left
hemisphere
Right
hemisphere
Time: 0 hours
Time: 1 hour
• Learning
– Process by which we acquire info as a result of
experience
• Memory
– Process by which information is encoded, stored,
retrieved
Peripheral Nervous System
• Consists of sensory receptors, nerves linking
receptors with CNS, nerves linking CNS with
effectors
• Somatic system (of PNS)
– Helps body response to changes in external
environment
– Maintain body’s posture and balance
– Cranial nerves – 12 pairs
• Emerge from brain
• Smell, sight, hearing, taste
Fig. 49-7-2
PNS
Afferent
(sensory) neurons
Efferent
neurons
Autonomic
nervous system
Motor
system
Locomotion
Sympathetic
division
Parasympathetic
division
Hormone
Gas exchange Circulation action
Hearing
Enteric
division
Digestion
– Spinal nerves – 31 pairs
• Emerge from spinal cord
• Named for general region of vertebral column from
which they originate
• 8 pairs cervical
• 12 pairs thoracic
• 5 pairs lumbar
• 5 pairs sacral
• 1 pair coccygeal
• Each one has dorsal root and ventral root
– Dorsal root
• Info from sensory receptors to spinal cord
– Ventral root
• Info leaves spinal cord to muscles and glands
• Autonomic system
– Helps maintain homeostasis in internal
environment
– Regulates heart rate, maintain constant body
temp.
– Works automatically, involuntary
– Effectors = smooth and cardiac muscle, glands
– Functionally organized into reflex pathways
– Receptors in viscera relay info to CNS
• Efferent portion of autonomic system (away
from CNS)
– Sympathetic and parasympathetic
•
•
•
•
•
Opposite effects
Ex: heart rate sped up – sympathetic
Heart rate slowed – parasympathetic
Sympathetic – stimulates organs, mobilize energy
Parasympathetic – conserve and restore energy
• Autonomic
– Preganglionic neuron
• 1st neuron
• Has cell body and dendrites in CNS
• Axon (peripheral nerve) ends by synapsing with a
– Postganglionic neuron
• Dendrites and cell body are in ganglion outside CNS
• Axon terminates near/on effector