chapter10 - nervous sytem
DESCRIPTION
HH126/MED115 Anatomy/Physiology Chapter 10 PowerPointTRANSCRIPT
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Chapter 10
The Nervous SystemThe Nervous System
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Divisions of the Nervous Divisions of the Nervous SystemSystem
Central nervous Central nervous systemsystem Consists of brain
and spinal cord
Peripheral nervous Peripheral nervous systemsystem Consists of nerve
network
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
NeurogliaNeuroglia
OligodendrocytesOligodendrocytes: Form myelin sheath Ependymal cellsEpendymal cells: Secrete cerebrospinal
fluid MicrogliaMicroglia: Perform phagocytosis AstrocytesAstrocytes: Form blood–brain barrier Schwann cellsSchwann cells: Form myelin sheath in
peripheral nervous system
Supportive cells of the nervous systemSupportive cells of the nervous system
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Blood–brain barrierBlood–brain barrier
Formed as astrocytes wrap around capillaries
Protects brain from foreign substances
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
The most numerous of all glial cells are:
A.microglia.B.astrocytes.C.Schwann cells.D.ependymal cells.
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Correct answer: B
Rationale:Astrocytes are pervasive throughout the brain and form the blood–brain barrier.
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
NeuronsNeurons Handle communication Three classes:
Sensory (afferent) neuronsSensory (afferent) neurons: Detect stimuli
InterneuronsInterneurons: Connect pathways Motor (efferent) neuronsMotor (efferent) neurons: Relay
messages
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Neuron structureNeuron structureCell body
Dendrites
Axon
Myelin sheath
Nodes of Ranvier
Synaptic knob
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Myelin sheathMyelin sheath
Peripheral Nervous SystemPeripheral Nervous System Central nervous systemCentral nervous system
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Which neurons detect sensations (such as touch or heat) and relay information about the stimuli to the central nervous system?
A.Efferent neuronsB.InterneuronsC.Afferent neuronsD.Schwann cells
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Correct answer: C
Rationale:Efferent neurons are motor neurons and relay messages from the brain to muscles and gland cells. Interneurons connect incoming sensory pathways with outgoing motor pathways in the central nervous system. Schwann cells form the myelin sheath.
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Impulse conductionImpulse conduction Caused by an electrical current Membrane potentialMembrane potential: When ions with
opposite electrical charges are separated by a membrane
PolarizationPolarization: When a membrane has an excess of positive ions on one side and an excess of negative ions on the other
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Impulse conduction: Step 1Impulse conduction: Step 1Resting potentialResting potential
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Impulse conduction: Step 2Impulse conduction: Step 2DepolarizationDepolarization
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Impulse conduction: Step 3Impulse conduction: Step 3Action potentialAction potential
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Impulse conduction: Step 4Impulse conduction: Step 4RepolarizationRepolarization
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Impulse conduction: Step 5Impulse conduction: Step 5Refractory periodRefractory period
<View animation of nerve impulse conduction in unmyelinated fibers>
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Impulse conduction: Impulse conduction: Myelinated fibersMyelinated fibers
<View animation on "Impulse transmission in myelinated fibers">
1.1.
2.2.
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
What is another term for nerve impulse?
A.RepolarizationB.Resting potentialC.DepolarizationD.Action potential
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Correct answer: D
Rationale:
Repolarization is when the nerve cell restores its electrical balance in preparation for a new stimulus. Resting potential is when the neuron is resting but has the potential to react. Depolarization occurs as the membrane becomes more positive.
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
SynapsesSynapses
<View animation on "Synapses">
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Spinal Spinal cordcord
Cervical
Thoracic
Lumbar
Sacral
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Structure of the spinal cordStructure of the spinal cord
Gray matter
White matter
Epidural space
Central canal
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Attachment of spinal nervesAttachment of spinal nervesDorsal nerve root
Ganglion
Ventral nerve root
Spinal nerve
Pia mater
Subarachnoidspace
Arachnoid mater
Dura mater
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Spinal tractsSpinal tracts
Dorsal column
Spinocerebellar tract
Spinothalmic tract
Corticospinal tracts
Extrapyramidal tractsExtrapyramidal tracts
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive ApproachSpinaSpina
l l nervenervess
• Relay information from spinal cord to rest of body
NerveFascicle
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Spinal Spinal nervesnerves
8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal
Cervical plexus
Brachial plexus
Lumbar plexus
Sacral plexus
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Somatic reflexesSomatic reflexes
<View animation on "Somatic reflexes">
11
22 33
44
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Bundles of axons within the white matter that serve as routes of communication to and from the brain are called:
A.ganglions.B.fascicles.C.tracts.D.plexuses.
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Correct answer: C
Rationale:Ganglions are cell bodies of the dorsal neurons clustered in a knot-like structure. Fascicles are bundles of nerve fibers contained within a nerve. Plexuses are nerve networks outside the spinal cord.
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Regions of the brainRegions of the brain
Cerebrum
Diencephalon
CerebellumMidbrain
Pons
Medulla oblongata
Brainstem
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Meninges of the brainMeninges of the brain
Dural sinus
Subdural space
Subarachnoid space
Falx cerebri
Dura mater
Arachnoid mater
Pia mater
Skull
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
VentriclesVentricles
Lateral ventricles
Third ventricle
Fourth ventricle
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Cerebrospinal fluidCerebrospinal fluid
<insert link to animation of “Formation and flow of CSF”>
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Which statement about gray matter is true?
A.It is charged with thought, learning, and reasoning.B.It forms the interior of the brain.C.It consists of myelinated fibers.D.It secretes cerebrospinal fluid.
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Correct answer: A
Rationale:Gray matter covers the surface of the brain, and it consists of unmyelinated fibers. The choroid plexus secretes cerebrospinal fluid.
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
BrainstemBrainstem
Midbrain
Pons
Medulla obtongata
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
CerebellumCerebellum
Cerebellum
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
DiencephalonDiencephalon
Thalamus
Hypothalamus
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Reticular activating systemReticular activating system
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
The cardiac and respiratory centers are found in the:
A.pons.B.cerebellum.C.diencephalon.D.medulla oblongata.
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Correct answer: D
Rationale:The pons conveys signals to and from other parts of the brain. The cerebellum monitors body movement. The diencephalon houses the thalamus and hypothalamus.
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
CerebrumCerebrum
Frontal lobeFrontal lobe
Temporal lobeTemporal lobe
Parietal lobeParietal lobe
Occipital lobeOccipital lobe
Insula
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Inside the cerebrumInside the cerebrum
White matter
Corpus callosum
Cerebral cortex
Basal nuclei
Spinal tracts
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Limbic systemLimbic system The “emotional brain” HippocampusHippocampus: Converts short-term
memory into long-term memory AmygdalaAmygdala: Stores and can recall
emotion
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Sensory functions of theSensory functions of thecerebral cortexcerebral cortex
Postcentral gyrus
Somatic sensory association area
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Motor functions of theMotor functions of thecerebral cortexcerebral cortex
Precentral gyrus
Motor association area
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
LanguageLanguageSequence of events required to read aloudSequence of events required to read aloud
11
2233
44
55
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
The limbic system is charged with:
A.emotion and learning.B.identifying the location of pain.C.planning muscle movements to form words.D.determining muscle movements to perform a task.
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Correct answer: A
Rationale:The somatic sensory association area allows us to pinpoint the location of pain. Broca’s area plans muscle movements to form words. Neurons in the motor association area determine the movements required to perform a task.
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Special sensesSpecial sensesPrimary gustatory complex
Primary visual cortex
Visual association area
Olfactory association area
Auditory association area
Primary auditory complex
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
SleepSleep Stage 1Stage 1: Drowsiness Stage 2Stage 2: Light sleep Stage 3Stage 3: Moderate to deep sleep Stage 4Stage 4: Slow-wave sleep REM sleepREM sleep: Dream sleep
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Cerebral lateralizationCerebral lateralization
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Cranial Cranial nervesnerves< View animation on "Cranial Nerves">
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Autonomic nervous systemAutonomic nervous system Regulates activities that maintain
homeostasis Sends impulses to cardiac and
smooth muscle Also called visceral motor system
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Visceral reflexesVisceral reflexes
<View animation of “Visceral (somatic) reflex arc">
11
2233
44
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Autonomic vs. somatic Autonomic vs. somatic pathwayspathways
Somatic pathwaySomatic pathway
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Autonomic vs. somatic Autonomic vs. somatic pathwayspathways
Autonomic pathwayAutonomic pathway
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Divisions of the autonomic Divisions of the autonomic nervous systemnervous system
SympatheticSympathetic: Prepares the body for activity
ParasympatheticParasympathetic: Calms body functions
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
SympathetiSympathetic divisionc division<View animation of "Structure of the sympathetic division">
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Adrenal Adrenal glandsglands
Play a role in sympathetic nervous system
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
ParasympathParasympathetic divisionetic division
<View animation of “Structure of the parasympathetic division”>
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
SYMPATHETIC PARASYMPATHETIC Originates in thoracolumbar
region Originates in craniosacral
region Ganglia lie in chain alongside
spinal cord Ganglia lie in or near target
organs Has short preganglionic and
long postganglionic fiber Has long preganglionic and short postganglionic fiber
Employs mostly norepinephrine as a
neurotransmitter (occasionally uses acetylcholine)
Employs acetylcholine as a neurotransmitter
Produces widespread, generalized effects
Produces local effects
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Which of the following is an action of the parasympathetic division of the autonomic nervous system?
A.Increase heart rate B.Constriction of bronchial tubesC.Stimulation of sweat glandsD.Inhibition of intestinal motility
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Correct answer: B
Rationale:The sympathetic division increases heart rate, stimulates sweat glands, and inhibits intestinal motility.
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
NeurotransmittersNeurotransmitters
Cholinergic fibersCholinergic fibers
Preganglionic fibers of sympathetic and parasympathetic divisions
Postganglionic fibers of parasympathetic division
Secrete acetylcholineacetylcholine
Adrenergic fibersAdrenergic fibers
Include most postganglionic fibers of the sympathetic division
Secrete norepinephrinenorepinephrine
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Cholinergic receptorsCholinergic receptors
Nicotinic receptorsNicotinic receptors
Occur within the adrenal medulla and the neuromuscular junction
Produce an excited response
Muscarinic receptors Muscarinic receptors
Occur on glands, smooth muscle, and cardiac muscle cells of organs innervated by cholinergic fibers
Produce a variable response
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Adrenergic receptorsAdrenergic receptors Cells with alpha-adrenergic receptorsalpha-adrenergic receptors
are excitedexcited by norepinephrine (NE). Cells with beta-adrenergic receptors beta-adrenergic receptors
are inhibitedinhibited by NE. <View animation of "Receptors of the
sympathetic and parasympathetic divisions">
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
The effect produced by a neurotransmitter is ultimately determined by:
A.the amount of neurotransmitter released.B.the type of neurotransmitter released.C.the type of receptor.D.the number of receptors.
Copyright © 2012 F.A. Davis Company
Understanding Anatomy & PhysiologyUnderstanding Anatomy & PhysiologyA Visual, Interactive ApproachA Visual, Interactive Approach
Correct answer: C
Rationale:The amount of neurotransmitter influences the strength (not type) of a response. Although the effect varies according to the type of neurotransmitter, the same neurotransmitter bound to a different receptor will have a different response. Therefore, it is the receptor that ultimately determines the response. The number of receptors influences the strength of the response.