Chapter 11- Nervous System II

PowerPoint Presentation to accompany Hole’s Human Anatomy and Physiology, 10th edition, edited by S.C. Wache for Biol2064.01

 You are responsible for the following figures and tables:Review Fig. 10.7. Differentiate CNS and PNS general tasks.Compare Fig. 11.5 - Structure of the CNS - the brain and spinal cord.Compare Tab. 11.9 and Fig. 11.29 - Components of the PNS Fig. 11.1 , 11.2 - meninges.Fig. 11.3, 11.4 - CSF. TB, blue box, p. 368Clinical Applications 11.1 - Spinal tap.Fig. 11.6 - Structure of the spinal cord.Fig. 11.7 - Define 'reflex arc‘.Fig. 11.8, 11.9 - Examples: Knee-jerk reflex, withdrawal reflex. Tab. 11.2 - Study the parts of a reflex arc.Fig. 11.15, Tab. 11.7 - CNS/ Brain structure - Read p.388-391, endocrine functions.Fig. 11.16 - Note fissures, sulci, gyri. Fig. 11.17, 11.18 - Areas of the cerebrum.Tab. 11.5 - Functions of the cerebral lobes.Fig. 11.25. PNS / Cranial nerves.Fig. 11.26. The vagus nerve # X, is important. Fig. 11.6.- CNS/ Spinal cord structure.Fig. 11.29 - PNS/ Spinal nerves - (see table in the attached lecture handout).Fig. 11.35 - ANS innervates smooth muscle and glands. Fig. 11.40 - sympathetic / parasympathetic nerves (see diagram in the attached lecture).

The meninges are membranes that protect the brain and the spinal cord

•Dura mater: outermost layer, composed of tough, white, dense connective tissue

•Arachnoid mater: thin, weblike membrane, subarachnoid space contains the cerebrospinal fluid

•Pia mater: thin membrane with nerves and blood vessels, attached to the brain and spinal cord

Meninges

Ventricles

The ventricles are a series of interconnected cavities

continuous with the central canal of the spinal cord which

transport the cerebrospinal fluid (CSF).

• Lateral ventricles: first and second ventricles located in the cerebrum

• Third ventricle: located in the midbrain, connected to the fourth ventricle via the cerebral aqueduct

• Fourth ventricle: located in the brain stem

Cerebrospinal Fluid (CSF)

CSF is a clear fluid with high Na+ and glucose and low K+ concentration, compared to other body fluids.

• Choroid plexuses are specialized capillaries of the pia mater, secrete cerebrospinal fluid.

• 500 ml of CSF are secreted each day, but only 140 ml circulates, due to reabsorption through the arachnoid granulations.

Spinal Cord• It begins where nervous tissue leaves the cranium at

the foramen magnum.

• It tapers to a point near the first and second lumbar vertebrae. Below this is the filum terminale and the cauda equina.

• It consists of 31 segments each giving rise to a pair of spinal nerves.

• The cervical and lumbar enlargements give off nerves to the upper and lower limbs respectively.

Note dorsal and ventral roots.

• Anterior median fissure and posterior median sulcus are grooves dividing the cord into right and left halves.

• Gray butterfly is the inner gray matter consisting of interneurons.

• Anterior and posterior horn are the wings. Between them is the lateral horn.

• The gray commissure connects the wings.

• The central canal contains CSF.

• The white matter contains the myelinated nerve tracts.

Spinal Cord

Reflex ArcsDefinition: The simplest nerve pathway is a reflex arc

which is autonomically controlled.

• Reflexes whose arcs pass through the spinal cord are spinal reflexes.

• Reflexes are autonomic and subconscious.

• They help maintain homeostasis by controlling heart rate, breathing rate, etc.

• They carry out automatic actions such as swallowing, sneezing, coughing, vomiting.

Note the pathway that the impulse travels.

neuron

neuron

neuron

neuron

Parts of a Reflex Arc

• Receptor: sensitive to a specific change

• Sensory neuron: transmits nerve impulse from the receptor to brain or spinal cord

• Interneuron: processing, conducts impulse from sensory to motor neuron

• Motor neuron: transmits nerve impulse from CNS out to effector (muscle or gland)

• Effector: responds to stimulation and produces the reflex action

(Fig. 11.8)

Note the pathway that the impulse travels.

neuron

neuron

Knee-jerk Reflex (Fig. 11.8)

• The knee-jerk or patellar tendon reflex is a monosynaptic reflex involving only two neurons.

• Striking the patellar ligament pulls the quadriceps femoris group and activates stretch receptors.

• The sensory neurons activate interneurons which transmit the impulse to a motor neuron.

• The motor neuron innervates the quadriceps femoris which contracts, extending the leg.

Note the pathway that the impulse travels.

neuron

neuron

neuronneuron

Withdrawal Reflex (Fig. 11.9)

Occurs in response to touching something painful,

such as pricking the finger.

• Sensory impulses are activated by pressure receptors in the skin and send a message to the spinal cord.

• Interneurons are stimulated and synapse with motor neurons.

• Motor neurons signal flexor muscles.

Crossed Extensor Reflex (Fig. 11.10)

Occurs with the withdrawal reflex. This reflexis due to interneurons within the reflex center of the spinal cord.

• Flexors are inhibited on the affected side (ipsilateral).

• Extensors are stimulated on the opposite side (contralateral) allowing body weight to be supported.

Spinal Cord Nerve Tracts (Fig. 11.11) Spinal cord ascending and descending nerve tracts:• Ascending and sensory - conduct impulses to the

brain.Anterior/Posterior spino-cerebellar tractAnterior/ Lateral spino-thalamic tractMedial reticulo-spinal tract

• Descending and motor - conduct motor impulses from the brain to muscle and glands.Anterior/ Lateral cortico-spinal tractAnterior/ Lateral reticulo-spinal tract

Note decussation area.

• Cerebral hemispheres: largest part• Corpus callosum: connects the hemispheres• Falx cerebri: dura mater separating the hemispheres• Gyri: convolutions or ridges in hemispheres

• Sulci: shallow grooves between gyri• Fissures: deep grooves between gyri

Cerebrum (Figure 11.15)

Cerebral Lobes (Figure 11.16)• Lobes: frontal, parietal, temporal, occipital • Insula: the lobe in the center of the cerebral hemisphere

that is situated deeply between the lips of the sylvian fissure -- called also central lobe, island of Reil

Note the lobes, fissures and sulci.

cerebellum

Brain Areas and Their Functions (Tab. 11.5)

Region of Brain Function

lateral ventricle hippocampus / internal frontal lobe areas

short-term memory processing, limbic system (emotions and motivation)

thalamus is part of the diencephalon integrates neurons for short-term memory

hypothalamus concerned autonomic functions, limbic system

frontal lobe primary olfactory area, Broca’s speech motor area

parietal lobe / along lateral sulcus gustatory area

temporal lobe Wernicke’s speech comprehension area; primary auditory / hearing association area

occipital lobes visual association area / perceptions

Cerebral Functions (Fig. 11.16)

• Broca’s area: motor speech area• Frontal eye field: voluntary eye movements• Motor areas: primary motor areas contain

pyramidal cells and contain synapses with descending spinal tracts.

• Sensory Areas: contain synapses from ascending tracts

• Association Areas: regions rich in interneurons that are neither motor or sensory, but interconnect with each other and other centers.

• General interpretative area (Wernicke’s area): complex thought processing

Cerebral Functions

Cerebral Lobes (Figure 11.18)

Fig. 11.18

• Frontal lobes: motor areas for voluntary skeletal muscles, association areas• Parietal lobes: sensory areas of temperature, touch, pressure, pain, speech association• Temporal lobes: sensory area for hearing, sensory association areas• Occipital lobes: sensory area for vision, visual association area

Cerebral Lobe Functions

Hemisphere Dominance

• Both hemispheres participate in basic functions.

• One side is usually the dominant hemisphere for some functions.

• For 90% of the population the left side is dominant for language-related activities of speech, writing, reading.

Coronal Cut - Left Cerebral Hemisphere (Fig.11.19)

Memory

• Short-term memory: patterns of synapses that change;

no permanent synapses formed.• Lateral ventricle hippocampus / internal frontal

lobe areas: short-term memory processing. • Limbic system (emotions and motivation): thalamus

integrates neurons for short-term memory

• Long-term memory:

patterns of synapses that remain unchanged.

Basal Nuclei• Basal Nuclei: masses of gray matter which consists of

unmyelinated interneurons within the cerebral hemispheres

• Hippocampus: a curved elongated ridge that is an important part of the limbic system, extends over the floor of the descending horn of each lateral ventricle of the brain, and consists of gray matter covered on the ventricular surface with white matter;a region of the cerebral cortex that performs repeated stimulations to strengthen synapses.

• Caudate nucleus, putamen, globus pallidus: Relay motor impulses and produce the inhibitory neurotransmitter, dopamine

Diencephalon• Thalamus: gateway for sensory impulses

• Hypothalamus: controls anterior pituitary which, in turn, controls effector glands

• Posterior and anterior pituitary gland (controls a variety of effector endocrine glands) attached to the hypothalamus via the infundibulum

• Optic tract and optic chiasma (cranial sensory nerve II)

• Mammillary bodies

• Pineal gland releases melatonin which controls the biorhythm / circadian rhythm

Limbic System

• Composed of portions of the cerebral cortex, thalamus, hypothalamus, basal nuclei, and other deep nuclei

• Controls emotional experiences

• Produces feelings of fear, anger, pleasure

• Interprets sensory impulses of smell / olfactory sense

Brain Stem-Midbrain• Connects brain stem and spinal cord with the CNS

• Cerebral peduncles: motor and sensory pathways

• Red nucleus: posture reflexes

• Corpora quadrigemina– Superior colliculi: visual reflexes

– Inferior colliculi: auditory reflexes

Fig. 11.20

midbrain

Medulla oblongata

Brain Stem-dorsal view (Fig. 11.20)

Brain Stem• Midbrain: the middle division of the three primary divisions of

the adult brain that includes a ventral part with the cerebral peduncles and a dorsal part with the corpora quadrigemina and that surrounds the aqueduct of Sylvius connecting the third and fourth ventricles

• Pons: sensory impulses relayed to brain, works with the medulla oblongata

• Medulla Oblongata: ascending and descending tracts pass through; contains the cardiac center which controls heart rate; contains the vasomotor center which controls blood pressure; contains the respiratory center which controls rate, rhythm, depth of breathing;corticospinal tract: any of four columns of motor fibers of which two run on each side of the spinal cord and which are continuations of the pyramids of the medulla oblongata : PYRAMIDAL TRACT: a : LATERAL CORTICOSPINAL TRACT

b : VENTRAL CORTICOSPINAL TRACT

Reticular Formation (shown in green): • Extends from the superior portion of the spinal cord into the diencephalon• Activates the cerebral cortex into a state of wakefulness• Filters incoming sensory impulses and regulates motor activities

Cerebellum

• Integrates sensory information concerning positions of body parts, coordination of skeletal muscle activity, maintain posture

• Two lateral hemispheres separated by the falx cerebelli, a layer of dura mater; the Vermis connects the hemispheres

• Cerebellar cortex: gray matter on outside• Arbor vitae: treelike pattern of white matter• Cerebellar peduncles: - inferior

- middle - superior

Fig. 11.22

Arbor vitae- ‘tree of life’

Peripheral Nervous System

Cranial nerves and spinal nerves:

• Somatic Nervous System: nerves that connect CNS to skin and skeletal muscles

• Autonomic Nervous System: nerves that connect CNS to viscera, smooth muscle nad glands.

Fig. 11.24

Epineurium: outer layer of connective tissuePerineurium: sleeve of looser connective tissue surrounding a fascicleEndoneurium: loose connective tissue surrounding each nerve fibers

• Twelve pairs of nerves which originate from brain stem and cerebrum

• Pass through foramen magnum in the skull

• Mixed nerves and special senses; some motor nerves

Cranial Nerves• I: Olfactory: sense of smell• II: Optic: sense of vision• III: Oculomotor: eye movement, focusing• IV: Trochlear: eye movement• V: Trigeminal: mixed nerve - ophthalmic: sensory: accessory eye structures

- maxillary: sensory: teeth, gum, lip, face - mandibular: sensory: scalp, jaw, teeth, lip

• VI: Abducens: eye movement• VII: Facial: mixed: taste, facial expression• VIII: Vestibulocochlear - vestibular branch: sense of equilibrium

- cochlear branch: sense of hearing

• IX: Glosspharyngeal: mixed: pharynx• X: Vagus: mixed: speech, swallowing, autonomic nervous system to viscera

• XI: Accessory: - cranial branch: motor to pharynx and larynx - spinal branch: motor to neck and back

• XII: Hypoglossal: tongue movement

Spinal Nerves

Thirty-one pairs of 2-inch long mixed nerves which

originate from the spinal cord and provide communication

between the spinal cord and the peripheral nerves which

transport impulses to the periphery of the human

body.

AM-PS:• Ventral (anterior) root: motor• Dorsal (posterior) root: sensory; dorsal root ganglion =

cell bodies of sensory nerves

• Cervical nerves: 8 pairs, C1-C8• Thoracic nerves: 12 pairs, T1-T12• Lumbar nerves: 5 pairs, L1-L5• Sacral nerves: 5 pairs, S1-S5• Coccygeal nerves: 1 pair, C0

Fig. 11.30

Plexuses• Cervical: first four cervical nerves [C1-C4]

• Brachial: lower four cervical nerves and first thoracic nerve [C5-C8 and T1]

• Lumbosacral: last thoracic nerve and lumbar, sacral, and coccygeal nerves [T12-S5]

PNS - Autonomic Nervous System

• Functions independently, involuntary / subconscious control

• Controls visceral activities by regulating smooth and cardiac muscles and glands

• Regulates heart rate, blood pressure, breathing, body temperature and other homeostatic mechanisms

• Responds to stress

Note: nerve cells are neurons. Note the spelling !!!Also note the pathway that the impulse travels !

Sympathetic Division of Motor Nerves

Fig. 11.37 – note the dorsal and ventral roots.

Fig. 11.36 – note the meninges, dorsal and ventral roots. Note that the spinal nerves are mixed function nerves [AM-PS].

Parasympathetic Division of Motor Nerves

• Fibers arise from brain stem and sacral spinal cord.

• The vagus nerve (X) carries 75% of the parasympathetic fibers.

• Fibers travel to terminal ganglia close to viscera.

• Postganglionic fibers travel to specific muscles or glands.

Neurotransmitters (Tab. 11.10)

Acetylcholine functions to maintain homeostasis.

Preganglionic fibers are cholinergic and secrete acetylcholine:

• Preganglionic sympathetic fibers of the ANS arise from the thoracic and lumbar regions of the spinal cord.

• Preganglionic parasympathetic fibers of the ANS arise from the brain and sacral region of the spinal cord.

Postganglionic parasympathetic and sympathetic fibers of sweat glands are also

cholinergic.

Norepinephrine and epinephrine function to

respond to stress

All other postganglionic sympathetic fibers are adrenergic and secrete norepinephrine

Fig. 11.38 – ANS preganglionic sympathetic fibers arise from

the thoracic and lumbar regions of the spinal cord.

Fig. 11.40 – ANS preganglionic parasympathetic fibers arise

from the brain and sacral region of the spinal cord.

Neurotransmitter Receptors• Acetylcholine binds to two cholinergic

receptors:– muscarinic receptors: effector cells at

parasympathetic postganglionic terminals– nicotinic receptors: synapses between pre- and

postganglionic fibers and at neuromuscular junctions of skeletal muscles

• Epinephrine and norepinephrine bind to two adrenergic receptors:- alpha and beta receptors, which give different responses at the target organ

Fig. 11.40 – note that most sympathetic fibers in the thoracic and lumbar regions are adrenergic and secrete norepinephrine / epinephrine

• Programmed cell death (apoptosis) begins at birth and is a natural control point within the cell cycle (Go, G1, S, G2, mitosis/meiosis, apoptosis or Go).

• Loss of neurons does not always mean loss of function.

• Signs of aging: fading memory, slowed responses and reflexes, and other changes.

Life-Span Changes