Nervous system Chapters 48-49

Nervous system

Chapters 48-49

Fig. 48-1

Nervous system organization

CNS (central nervous system) Brain Spinal cord

Nervous system organization PNS (peripheral nervous system) Sensory & motor neurons Somatic motor neurons Stimulate skeletal muscles Autonomic motor neurons Regulate smooth & cardiac muscle, & glands Sympathetic/parasympathetic Counterbalance

Types of neurons Sensory neurons: (afferent neurons) Carry impulses to the CNS Motor neurons: (efferent neurons) Carry impulses from the CNS to effectors

(muscles or glands) Interneurons: (association neurons) Located in brain & spinal column Higher functions or more complex reflexes Learning & memory

Fig. 48-3

Sensor

Sensory input

Integration

Effector

Motor output

Peripheral nervoussystem (PNS)

Central nervoussystem (CNS)

Neuron structure

Cell body Contains nucleus & organelles Dendrites Branched, receives signals Axon Single, send signals Axon hillock: where signals are generated

Neuron structure Synapse Site of communication between cells Presynaptic Transmitting neuron Postsynaptic Receiving cell Neurotransmitters Chemical messengers

Neuron structure

Glia “glue” Supporting cells Supply nutrients Remove wastes Guiding axon migration Immune functions

Membrane potential

Electrical charge across membrane of cell Cytoplasm is negative compared to

extracellular fluid Unequal distribution of anions & cations Either side of the membrane Ranges from –50 to –200 millivolts (mV)

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Resting membrane potential Neurons are not stimulated, not transmitting

signals 1. Fixed anions Proteins, carbohydrates & nucleic acids More abundant inside 2. Sodium/potassium pump

– 2K+ into cell/3Na+ out of cell 3. Ion leak channels Allows K+ to move out more than Na+ to move in Nerve cells –50 to –70 mV

Resting potential

OUTSIDECELL

[K+]5 mM

[Na+]150 mM

[Cl–]120 mM

INSIDECELL

[K+]140 mM

[Na+]15 mM

[Cl–]10 mM

[A–]100 mM

(a)

Action potentials

Signals in the nervous system Sudden change in membrane voltage Change in membrane permeability to

ions Due to stimuli

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Action potential

Ligand-gated (chemical) channels: Change shape when chemicals bind to

them Neurotransmitters or hormones Voltage-gated ion channels: Open when change in membrane potential Axons

Action potentials Depolarization: Membrane potential less negative More positive ions flow in Na+1

Hyperpolarization: Membrane potential more negative Negative ions flow in (Cl-1) Positive ions flow out (K+1 or Na+1)

Action potentials

Threshold: Level of depolarization Produces an action potential All or none -55mV

Action potential

Nerve impulse Threshold Na & K voltage-gated ion channels opened First Na opens flows into cytoplasm (down concentration gradient) Potassium opens flows out Depolarizes the cell

Action potential

Cl flows into cell Hyperpolarizes Na channels close K channels remain open a little longer Overshoot (hyperpolarize) Resting potential obtained Occurs in 1-2 milliseconds along axons

Action potential

Action potential

Action potential

Axon

Plasmamembrane

Cytosol

Actionpotential

Na+

Actionpotential

Na+

K+

K+

ActionpotentialK+

K+

Na+

Action potential

Strong depolarizing stimulus

+50

Mem

bran

e po

tent

ial (

mV)

–50 Threshold

Restingpotential

–1000 2 3 4

Time (msec)

(c) Action potential

1 5

0

Actionpotential

6

Action potential

Do not loose amplitude Greater speed of conduction Greater diameter of axon Myelinated Nodes of Ranvier Interruptions of myelin sheaths

Action potential

Saltatory impulse: Jump from one node to another

Saltatory impulse

Action potential 2 types of neuroglia Produce myelin sheaths Multiple layers of membrane around axon Insulation Schwann cells PNS Oligodendrocytes CNS

Synapses 2 types of synapses 1. Electrical Gap-junctions Membrane potentials change quickly 2. Chemical Neurotransmitters Most vertebrates

Synapses

Synaptic cleft: Space between pre & postsynaptic cell Synaptic vesicles: Located at end of axon Contain neurotransmitters

Synapses

Impulse down axon Causes rapid influx of Ca ions Synaptic vesicles to bind plasma membrane Releases neurotransmitters by exocytosis Neurotransmitters bind postsynaptic

receptor proteins Response depends on neurotransmitters

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Types of neurotransmitters Acetylcholine Amino acids

– Glutamate– Glycine– GABA (gamma-aminobutyric acid)

Biogenic amines– Epinephrine (adrenaline)– Dopamine– Norepinephrine– Serotonin

Gases– NO

Table 48-1

Acetylcholine (ACh)

First discovered Synapse between motor neuron & a

muscle fiber Neuromuscular junction Binds postsynaptic membrane Causes ion channels to open Stimulates muscle contraction

Acetylcholine Acetylcholinesterase (AChE) Enzyme located on postsynaptic membrane Enzyme cleaves ACh to be inactive Muscle relaxes Nerve gas & insecticide parathion Inhibitors of AChE Causes spastic paralysis Respiratory muscles causes death

Acetylcholine

Other synapses Usually between neurons Postsynaptic membrane is on dendrites

or cell body of another neuron Myasthenia gravis Alzheimers

Acetylcholine

Nicotine Affinity for Ach receptors Botulism Prevents pre-synaptic release of Ach BOTOX

EPSPs Excitatory postsynaptic potentials Towards threshold IPSPs Inhibitory Postsynaptic Potential Away threshold

Glutamate

Excitatory in CNS Normal amounts stimulate Excessive amounts show neuro

degeneration Huntington’s chorea

GABA and glycine

Inhibitory in CNS Neural control of body movements Other brain functions Valium (diazepam) sedative Increases GABA to bind receptor sites Increases GABA’s effectiveness

Biogenic amines Epinephrine (adrenaline), norepinephrine

& dopamine Derived from tyrosine (aa) Dopamine Controls body movements (CNS, PNS) Excitatory Tremors, Parkinson disease Decrease in neurons releasing dopamine

Biogenic amines

Serotonin derived from tryptophan (aa) Inhibitory (CNS) Sleep, mood, attention and learning Decreased serotonin causes depression Prozac blocks uptake after release LSD binds receptors for serotonin

Gas

Nitric oxide (NO) Not stored Generated from arginine when needed PNS Smooth muscle relaxation

Neuropeptides Polypeptides released by axons at synapses Substance P CNS, affects perception of pain Endorphins/Enkephalins Released in CNS Block perception of pain Opiates: morphine & heroin Similar in structure to neurotransmitters Bind receptor sites (pain-reducing)

Fig. 49-2

(e) Insect (arthropod)

Segmentalganglia

Ventralnerve cord

Brain

(a) Hydra (cnidarian)

Nerve net

Nervering

Radialnerve

(b) Sea star (echinoderm)

Anteriornerve ring

Longitudinalnerve cords

(f) Chiton (mollusc) (g) Squid (mollusc)

Ganglia

BrainGanglia

(c) Planarian (flatworm)

Nervecords

Transversenerve

Brain

EyespotBrain

(d) Leech (annelid)

Segmentalganglia

Ventralnervecord

Brain

Spinalcord(dorsalnervecord)

Sensoryganglia

(h) Salamander (vertebrate)

Fig. 49-4

Peripheral nervoussystem (PNS)

Cranialnerves

Brain

Central nervoussystem (CNS)

GangliaoutsideCNS

Spinalnerves

Spinal cord

Vertebrate Nervous System

CSF Cerebral spinal fluid Bathes brain, protects, provides nutrients Meninges Connective tissues that surround the

brain

CSF

Hydrocephalus

Meninges

NS

White matter Myelinated axons Gray matter Unmyelinated axons

Glia CNS Astrocytes Support, increase blood flow, NT Oligodendrocytes Myelination Ependymal cell Line ventricles, CSF flow Microglial Defend against microorganisms

glia

Oligodendrocyte

Microglialcell

Schwann cells

Ependy-malcell

Neuron Astrocyte

CNS PNS

Capillary

(a) Glia in vertebrates

VENTRICLE

Brain

3 divisions in vertebrates (embryo) Hindbrain Cerebellum, medulla oblongata, pons Midbrain Forebrain Cerebrum, thalamus, hypothalamus,

basal ganglia, limbic system

Brain

Brain

Cerebrum

Divided right & left cerebral hemispheres Connected by corpus callosum (band of

axons) Each hemisphere Cerebral cortex Internal white matter Basal nuclei (neurons in the white matter)

Fig. 49-13

Corpuscallosum

Thalamus

Left cerebralhemisphere

Right cerebralhemisphere

Cerebralcortex

Basalnuclei

Cerebrum

Divided further into four lobes Occipital lobe: vision Parietal lobe: body sensations, spatial

and visual perceptions Frontal: thought processing, behavior Temporal: hearing, understanding

language

Cerebrum

Cerebral cortex

Gray matter Outside of cerebrum Gyri: folds of nerves cells Sulcus: grooves or crease Functional areas in the cortex Sensory, motor or associative

Cerebral cortex

Sensory information comes to cortex Via the thalamus Primary sensory areas in different lobes Processed in association areas Motor command

Fig. 49-15

Speech

Occipital lobe

Vision

Temporal lobe

Frontal lobe Parietal lobe

Somatosensoryassociationarea

Frontalassociationarea

Visualassociationarea

ReadingTaste

Hearing

Auditoryassociationarea

Speech

Smell

Mot

or c

orte

xSo

mat

osen

sory

cor

tex

Thalamus

Controls sensory information Visual, auditory & somatosensory

information Relays information to lobes of cortex

Basal Ganglia (nuclei)

Located in white matter of cerebrum Receives sensory information Receives motor commands from cortex

and cerebellum Participates in body movements

Limbic system

Located deep in the cerebrum Deals with emotions

Fig. 49-18

ThalamusHypothalamus

Prefrontalcortex

Olfactorybulb

Amygdala Hippocampus

Cerebellum

Coordination Balance and posture Hand-eye coordination

Hypothalamus

Controls visceral activities Regulates body temperature Hunger, thirst Emotional states Regulates the pituitary gland Regulates many endocrine glands

Brainstem

Medulla oblongata Controls various visceral activities Breathing, pulse, BP, swallowing Connects spinal cord to brain Pons Connects cerebellum & cerebrum to brain Nerves to eyes and face

Spinal cord Inner zone: Gray matter Cell bodies of interneurons, motor neurons &

neuralgia Outer zone: White matter Dorsal columns are sensory neurons Ventral columns are motor neurons Relay messages

Spinal cord

Reflexes Sensory neuron to motor neuron Spinal column Quick response Knee jerk

Reflexes

PNS

Transmits information to - from CNS Cranial nerves Extend from brain Affect head, neck regions Spinal nerves Originate in spinal cord Extend to areas below head

Spinal nerves

PNS Somatic nervous system (skeletal muscles) Autonomic nervous system (smooth, cardiac

muscles & glands) Sympathetic Originate in the thoracic or lumbar regions Epinephrine or norepinephrine Parasympathetic Originate in the brain or sacral region Acetylcholine

CT scan

PET scan