Lecture 8. Regulatory Mechanisms

I. Intercellular Communication and the Endocrine System

II. Nervous Coordination

• detection of external and internal stimuli

• control and coordination of responses to stimuli

• includes the brain, spinal cord, sense organs

Nervous System

• sensory or afferent neuron• motor or efferent neuron• interneuron

Neurons: Functional Units of Nervous System

Neurons: Functional Units of Nervous System

Neuroglia•also known as glial cells•non-neuronal cells that maintain homeostasis, form myelin, and provide support and protection for the brain's neurons•i.e. astocyte, oligodendrocyte and microglia

Astrocyte•biochemical support of endothelial cells that form the blood-brain barrier •provision of nutrients to the nervous tissue •maintenance of extracellular ion balance•with principal role in the repair and scarring process of the brain and spinal cord following traumatic injuries.

Microglia•the resident macrophages of the brain and spinal cord, and thus act as the first and main form of active immune defense in the central nervous system

Oligodendrocyte•insulation of axons in the central nervous system (the brain and spinal cord) of higher vertebrates•provision of nutrients to the nervous tissue

Patterns of Organization of Nervous System

• Nerve nets

Patterns of Organization of Nervous System

• with cephalization come more complex nervous systems

• every cell has a voltage or membrane potential across its plasma membranes

• a membrane potential is a localized electrical gradient across membrane– anions are more concentrated within a cell– cations are more concentrated in the extracellular

fluid

Nature of Nerve Signals

• Measuring Membrane Potentials

• an unstimulated cell usually has a resting potential of -70mV

• How a Cell Maintains a Membrane Potential– Cations

• K+ the principal intracellular cation

• Na+ is the principal extracellular cation

– Anions• proteins, amino acids, sulfate, and phosphate are the

principal intracellular anions

• Cl– is principal extracellular anion

• Ungated ion channels allow ions to diffuse across the plasma membrane– these channels are always open

• this diffusion does not achieve an equilibrium since Na-K pump transports these ions against their concentration gradients

• changes in membrane potential of a neuron give rise to nerve impulses

• excitable cells have the ability to generate large changes in their membrane potentials– gated ion channels open or close in response to

stimuli• the subsequent diffusion of ions leads to a change in the

membrane potential

• Types of gated ions:– chemically-gated ion channels open or close in

response to a chemical stimulus– voltage-gated ion channels open or close in response

to a change in membrane potential

• Graded Potentials: Hyperpolarization and Depolarization– graded potentials are changes in membrane

potential

• Hyperpolarization– Gated K+ channels open

K+ diffuses out of the cell the membrane potential becomes more negative

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

• Depolarization.– Gated Na+ channels open

Na+ diffuses into the cell the membrane potential becomes less negative.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 48.8b

• The Action Potential: All or Nothing Depolarization– if graded potentials sum

to -55mV a threshold potential is achieved• triggers an action

potential– Axons only

• In the resting state closed voltage-gated K+ channels open slowly in response to depolarization

• Voltage-gated Na+ channels have two gates– closed activation gates open rapidly in response to

depolarization– open inactivation gates close slowly in response to

depolarization

• nerve impulses propagate themselves along an axon

• the action potential is repeatedly regenerated along the length of the axon

• Saltatory conduction– in myelinated neurons only unmyelinated regions of

the axon depolarize• thus, the impulse moves faster than in unmyelinated

neurons

• Electrical Synapses– action potential travels directly from the presynaptic

to the postsynaptic cells via gap junctions

• Chemical Synapses– more common than electrical synapses– postsynaptic chemically-gated channels exist for ions

such as Na+, K+, and Cl-• depending on which gates open the postsynaptic neuron

can depolarize or hyperpolarize

• Acetylcholine– excitatory to skeletal muscle– inhibitory to cardiac muscle– secreted by the CNS, PNS, and at vertebrate

neuromuscular junctions

Neurotransmitters

• Biogenic Amines– Epinephrine and norepinephrine• can have excitatory or inhibitory effects• secreted by the CNS and PNS• secreted by the adrenal glands

epinephrine norepinephrine

• Dopamine– generally excitatory; may be inhibitory at some

sites• widespread in the brain• affects sleep, mood, attention, and learning

– secreted by the CNS and PNS– a lack of dopamine in the brain is associated with

Parkinson’s disease– excessive dopamine is linked to schizophrenia

Parkinson’s disease

•degenerative disorder of the central nervous system that often impairs the sufferer's motor skills, speech, and other functions •characterized by muscle rigidity, tremor, postural abnormalities, gait abnormalities, a slowing of physical movement (bradykinesia) and a loss of physical movement (akinesia) in extreme cases

Schizoprenia

•mental disorder characterized by a disintegration of the process of thinking and of emotional responsiveness•auditory hallucinations, paranoid or bizarre delusions, or disorganized speech and thinking, and it is accompanied by significant social or occupational dysfunction

• Serotonin– generally inhibitory• widespread in the brain• affects sleep, mood, attention, and learning

– secreted by the CNS

• Amino Acids– Gamma aminobutyric acid (GABA)

• inhibitory• secreted by the CNS and at invertebrate

neuromuscular junctions

– Glycine• inhibitory• secreted by the CNS

• Amino Acids

– Glutamate• excitatory• secreted by the CNS and at invertebrate

neuromuscular junctions

– Aspartate• excitatory• secreted by the CNS

• Neuropeptides– Substance P• excitatory• secreted by the CNS and PNS

– Met-enkephalin (an endorphin)• generally inhibitory• secreted by the CNS

• Gases that act as local regulators– Nitric oxide– Carbon monoxide

Vertebrate Nervous System

• A ganglion is a cluster of nerve cell bodies within the peripheral nervous system.

• A nucleus is a cluster of nerve cell bodies within the central nervous system.

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Cranial and Spinal Nerves

• Brain and spinal cord– central canal is continuous with ventricles;

contain cerebrospinal fluid (CSF)–white matter is composed of bundles of

myelinated axons– gray matter consists of unmyelinated axons,

nuclei, and dendrites

• A Simple Nerve Circuit – the Reflex Arc in Vertebrates– A reflex is an autonomic response

(Foramen of Monro)

(Opticoel)

(Aqueduct of Sylvius or Iter)

– functions in homeostasis, coordination of movement, conduction of impulses to higher brain centers

– relays information to and from higher brain centers

• Midbrain– contains nuclei involved in the integration of

sensory information• superior colliculi are involved in the regulation

of visual reflexes• inferior colliculi are involved in the regulation of

auditory reflexes

• Medulla oblongata– contains nuclei that control visceral (autonomic

homeostatic) functions– breathing– heartbeat and blood pressure– swallowing– vomiting– digestion• Pons

– contains nuclei involved in the regulation of visceral activities such as breathing

Cerebellum

• functions for coordination of motor activities, and perceptual and cognitive factors• relays sensory information about joints, muscles, sight, and

sound to the cerebrum.• coordinates motor commands issued by the cerebrum

– Epithalamus• includes a choroid plexus and the pineal gland

pineal gland

thalamus

• relays all sensory information to the cerebrum• relays motor information from the cerebrum• receives input from the cerebrum• receives input from brain centers involved in the regulation

of emotion and arousal

hypothalamus

• regulates autonomic activity– contains nuclei involved in thermoregulation, hunger,

thirst, and sexual and mating behavior– regulates the pituitary gland

• in mammals, the hypothalamic suprachiasmatic nuclei (SCN) function as a biological clock

(outer covering of gray matter)

Cerebrum

• association areas (where sensory information is integrated and assessed and motor responses are planned)

(sensory reception and integration; taste)

(memory, emotion, planning, judgement and aggression)

(learning, memory, hearing, smell, visual recognition, emotional behavior)

• Lateralization of Brain Function– The left hemisphere• specializes in language, math, logic operations, and

the processing of serial sequences of information, and visual and auditory details

• specializes in detailed activities required for motor control

– The right hemisphere• specializes in pattern recognition, spatial

relationships, nonverbal ideation, emotional processing, and the parallel processing of information

• Language and Speech– Broca’s area

• usually located in the left hemisphere’s frontal lobe• responsible for speech production

– Wernicke’s area• usually located in the right hemisphere’s temporal lobe• responsible for the comprehension of speech

– Other speech areas are involved in generating verbs to match nouns, grouping together related words, etc

The Limbic System- hippocampus- olfactory cortex- inner portions of the cortex’s lobes- parts of the thalamus and hypothalamus

The Limbic System• mediates basic emotions (fear, anger), involved in

emotional bonding, establishes emotional memory– e.g., the amygdala is involved in recognizing the

emotional content of facial expression

• Memory and Learning– short-term memory stored in the frontal lobes– establishment of long-term memory involves the

hippocampus

• The transfer of information from short-term to long-term memory– enhanced by repetition– influenced by emotional states mediated by the

amygdala– Influenced by association with previously stored

information.

Cranial Nerves

• nerves that emerge directly from the brain

• In humans, there are 12 pairs of cranial nerves

• 1st and 2nd pair – cerebrum • 3rd – 12th pair – brainstem

Cranial Nerves

Cranial Nerves

Cranial Nerve TypeI. Olfactory SensoryII. Optic SensoryIII. Occulomotor MotorIV. Trochlear MotorV. Trigeminal BothVI. Abducent MotorVII. Facial BothVIII. Auditory SensoryIX. Glossopharyngeal BothX. Vagus BothXI. Accessory MotorXII. Hypoglossal Motor

Sensory Systems

• sensations begin as different forms of energy that are detected by sensory receptors–energy is converted to action potentials that

travel to appropriate regions of the brain

• Sensations are action potentials that reach the brain via sensory neurons.

• Perception is the awareness and interpretation of the sensation.

• Sensory reception begins with the detection of stimulus energy by sensory receptors.– Exteroreceptors detect stimuli originating outside

the body.– Interoreceptors detect stimuli originating inside the

body.– Sensory receptors convey the energy of stimuli into

membrane potentials and transmit signals to the nervous system.• involves sensory transduction, amplification,

transmission, and integration.

• Sensory Transduction– conversion of stimulus energy into a change in

membrane potential– Receptor potential: a sensory receptor’s version of

a graded potential

• Amplification– the strengthening of stimulus energy that can be

detected by the nervous system

• Transmission– the conduction of sensory impulses to the CNS– some sensory receptors must transmit chemical

signals to sensory neurons• the strength of the stimulus and receptor potential

affects the amount of neurotransmitter released by the sensory receptor

– some sensory receptors are sensory neurons• the intensity of the receptor potential affects the

frequency of action potentials

• Integration– the processing of sensory information.• begins at the sensory receptor

– sensory adaptation is a decrease in responsiveness to continued stimulation

– the sensitivity of a receptor to a stimulus will vary with environmental conditions

Categories of Sensory Receptors

• Mechanoreceptors respond to mechanical energy.– muscle spindle is an interoreceptor that responds

to the stretching of skeletal muscle.– hair cells detect motion

Pacinian corpuscle – mechanoreceptor in the skin that detects pressure and vibration

• Pain receptors = nocioceptors– different types of pain receptors respond to

different types of pain– Prostaglandins increase pain by decreasing a pain

receptor’s threshold

• Thermoreceptors respond to heat or cold– respond to both surface and body core

temperature

• Chemoreceptors respond to chemical stimuli.– general chemoreceptors transmit information

about total solute concentration– specific chemoreceptors respond to specific types

of molecules– internal chemoreceptors respond to glucose, O2,

CO2, amino acids, etc.– external chemoreceptors are gustatory receptors

and olfactory receptors

• Electromagnetic receptors respond to electromagnetic energy– Photoreceptors respond to the radiation we know

as visible light– Electroreceptors: some fish use electric currents to

locate objects

Photoreceptors and Vision

• Eye cups are among the simplest photoreceptors– detect light intensity and direction — no image

formation– the movement

of a planarian is integrated with photoreception

• Image-forming eyes– compound eyes of insects and crustaceans.

• Each eye consists of ommatidia, each with its own light-focusing lens.

• Single-lens eyes of invertebrates such as jellies, polychaetes, spiders, and mollusks– the eye of an octopus works much like a camera

and is similar to the vertebrate eye

Vertebrate Eye

• Accommodation is the focusing of light in the retina.– In squid, octopuses, and many fish this is

accomplished by moving the lens forward and backward.

– In mammals, accommodation is accomplished by changing the shape of the lens

• Photoreceptors of the human retina– About 125 million rod cells– About 6 million cone cells

• Rhodopsin (retinal + opsin) is the visual pigment of rods.

• The absorption of light by rhodopsin initiates a signal-transduction pathway.

• Visual processing begins with rods and cones synapsing with bipolar cells– Bipolar cells synapse with

ganglion cells• Visual processing in the retina

also involves horizontal cells and amacrine cells

• Vertical pathway: photoreceptors bipolar cells ganglion cells’ axons.

• Lateral pathways:– Photoreceptors horizontal cells other

photoreceptors.• Results in lateral inhibition.

– More distance photoreceptors and bipolar cells are inhibited sharpens edges and enhances contrast in the image.

– Photoreceptors bipolar cells amacrine cells ganglion cells.

• Also results in lateral inhibition, this time of the ganglion cells.

• The optic nerves of the two eyes meet at the optic chiasm.– Where the nasal half of each

tract crosses to the opposite side.• Ganglion cell axons

make up the optic tract.– Most synapse in the

lateral geniculate nuclei of the thalamus.• Neurons then convey

information to the primary visual cortex of the optic lobe.

Hearing and Equilibrium

• Vibrations in the cochlear fluid basilar membrane vibrates hair cells brush against the tectorial membrane generation of an action potential in a sensory neuron.

• Pitch is based on the location of the hair cells that depolarize.

• Volume is determined by the amplitude of the sound wave.

• the inner ear also contains the organs of equilibrium

• Statocysts are mechanoreceptors that function in an invertebrate’s sense of equilibrium.

• sound sensitivity in insects depends on body hairs that vibrate in response to sound waves– different hairs respond to different frequencies

• many insects have a tympanic membrane stretched over a hollow chamber

Chemoreception: Taste and Smell

• taste receptors in insects are located on their feet

• In mammals, taste receptors are located in taste buds, most of which are on the surface of the tongue.

• Each taste receptor responds to a wide array of chemicals.

• Sensory receptors transduce stimulus energy and transmit signals to the nervous system

• In mammals, olfactory receptors line the upper portion of the nasal cavity– the binding of odor molecules to olfactory receptors

initiate signal transduction pathways