Biology 12

Nervous System

Introduction

Allows us to sense internal and environmental stimuli, react to stimuli, move, storage of memories, the ability to know we exist, etc.

Basic component of nervous system is the _______ or _________ As cells they contain many organelles and cytoplasm similar to

those found in other cells

Neuronal Anatomy

Basic Parts of a Neuron:

a. Cell Body (soma) contains nucleus, cytoplasm and other organelles—e.g.

______________, Golgi body, microtubules, microfilaments, E.R., lysosomes etc.

also contains granular material alled _____ _____—many ribosomes and rough E.R.

b. Axon Thin tube-like process arising from cell body Typically only one per neuron cytoplasm in axon called ______________ No Nissl bodies or free ribosomes longer than dendrites contains most of cells cytoplasm

c. Axon Hillock Controls generation of action potential (i.e. nerve signal)

d. Dendrites Receive excitation from other cells branched fibers, spiny in appearance

2

carry signals toward cell body

Note: dendrites and axons are often called ______ or ________

e. Synaptic endings or synaptic bulbs— ends of axons that release transmitter substances to propagate signal to other neuron

Neuron Shapes

Are classified according to how many processes extend from cell

body (soma)

Neuron Functions:3

3 types of neurons exist based on their function: ______________, _____________________ and __________________

a. Sensory (afferent) neuron Brings nerve impulse from sensory organs to CNS

b. Motor (efferent) neuron

c. Interneuron (association neuron) Relays nerve impulses between neurons in CNS

Neuroglial Cells and Meylin Sheath

Neurons are often associated with other types of cells found only in N.S.—____________________________________

Different types of neuroglial cells provide nutrition, support, communication and protection between neurons

One type of neuroglial cell is called a __________________ (or neurolemnmocyte) found in PNS and ____________________ in CNS

Schwann cells and oligodendrocytes encircle axons many times with their membranes forming ____________________—rich in lipid

4

Neurolemma is outermost layer of Schwann cells surrounding neurons→ does not degenerate after nerve injury but forms template or tube for nerves to heal in PNS

Gaps between Schwann cells are called _____________________ Distance between Nodes of Ranvier are called an _______________ Because of myelin sheath, electrical current can only flow across

axoplasm at the nodes so speed of propagation of electrical signal is quick – ______________ _____________

Diagram of Schwann cell encircling axon

5

Generaration Of Action Potentials And Nerve Impulses

A. Resting Potential

Can measure __________________________ (voltage) between outside and inside of a neuron—using ______________

Find that the inside of an axon is negative compared to the outside---i.e. (-65 mV)

Neuron has a negative membrane potential at rest—called its _______ _______________

Outside ________________ has higher concentration of Na+ ions than inside _______________ and inside has higher concentration of K+ ions than outside—also, there is a much higher concentration of negative organic ions (proteins) inside the cell than outside

This increased permeability to K+ ions contributes to the negative

resting potential shown by neurons

6

Axomembrane more permeable to K+ ions than Na+ so more K+ tends to diffuse out than Na+ in which leads to a greater positive charge outside the cell than inside resulting in a neurons resting membrane potential

B. Action Potential

Stimulation of neuron causes axomembrane to increase its permeability to Na+ ions by opening up gates of Na+ channels→ Na+ move into cell due to concentration gradient and attraction to negative ions inside axon→ ________________ (charge inside membrane goes from “–“ to “+” charge

During above phase, cell is said to be in ____________________—another action potential cannot occur due to membrane potential being positive (1-2 ms)

7

Next, Na+ channels close and K+ ion gates in membrane open and K+ start to move outside of axon along concentration gradient and due to repulsive forces due to excess of positive charge inside axon→ restores negative charge inside membrane relative to outside (-65 mV)→ _________________

Notice that r.m.p. becomes more negative than normal—called __________________—due to K+ ions rushing out and making outside more positive than r.m.p. and inside more negative than r.m.p.

Na+/K+ pump subsequently return ions to their original positions Movement of above cycle of change across axomembrane constitutes

a _________________

Diagram of Action Potential

8

Transmission of Nerve Impulse Across Synapses

Each synaptic ending terminates in an axonal ending or ________ _________

These structures contain vesicles containing __________________

Synaptic cleft (20 nm) is gap between ___________________ and _____________________ (i.e. membrane of dendrite of other cell)

Note: sometimes gap junctions do exist between pre and post-synaptic membranes

Nerve impulse reaches pre-synaptic membrane → open Ca++ gates → Ca++ enters presynaptic bulb → variety of reactions occur causing→ vesicles to fuse to presynaptic membrane → neurotransmitter released into synaptic cleft → neurotransmitters diffuse across synaptic cleft→ neurotransmitter bind to receptors on post synaptic membrane → change in membrane potential of post synaptic cell which can result in excitation or inhibition of

9

post synaptic membrane (depends on neurotransmitter and receptor type)

If excitatory, neurotransmitters cause post-synaptic membrane potential to decrease (i.e. become less negative)—called _______ or excitatory post synaptic potential

If inhibitory, neurotransmitter causes post-synaptic membrane potential to increase (i.e. become more negative)—called _______ or inhibitory post synaptic potential

If EPSP is great enough to reach the ____________________ (-50 mV) and spread to the axon hillock, it results in an action potential

Summation Across Synapses

Whether a neuron fires or not depends on ____________

Figure showing summation:

10

In other words, if EPSP is big enough to depolarize the post-synaptic neuron to the ___________________ (about 15-20 mV less negative than resting potential) and spread to axon hillock a nerve impulse results

Once action potentials result they are all the same intensity for a given neuron—i.e. one action potential is not bigger or smaller than another— this is known as the ___________________ of neurons

Diagram of an Action Potential

11

Types of Neurotransmitters

Amino acids, peptides or even some gases such as NO or CO Some common transmitters are __________, ___________,

________________, ____________ and ________ Acetylcholine is a major neurotransmitter of PNS—e.g.

parasympathetic N.S. and motor neurons of PNS, but also found in CNS.

Once neurotransmitters released, they are quickly destroyed by enzymes in synapse or taken up by pre or post-synaptic membrane and repackaged or destroyed→ prevents overstimulation or over-inhibition of post synaptic membrane

_________________ is name of enzyme that breaks down AchE

12

________ (monoamine oxidases) break down NE and Serotonin or Dopamine

13

Diagram of Synapse:

14

Major divisions of nervous system exist:

a. Central Nervous System (CNS)

f. Peripheral Nervous System (PNS)

Made up of cranial, spinal nerves and nerves of the autonomic N.S.

Note: nerves are bundles of neurons with their cell bodies found in CNS or in ganglia (collection of nerve cell bodies) outside of CNS

PNS also divided into ________ (responsible for voluntary control) and _____________ (involuntary control) nervous system

15

Peripheral Nervous System—Cranial Nerves

12 pairs of Cranial nerves serving head, neck and face

Cranial nerves can be solely motor, sensory or mixed

Peripheral Nervous System—Spinal Nerves

Spinal nerves can be ________ (under voluntary control) or ______________ (under unconscious control)

16

Are connected to the spinal cord and come out between vertebrae of spine

Thus, spinal nerves are ______________________ having both motor and sensory neurons

Sensory fibres enter spinal cord via __________ _______ Motor fibres exit spinal cord via ___________ __________

Spinal nerves are responsible for reflex responses Involve both sensory and motor neurons Knee jerk reflex is example of spinal reflex

17

Diagram of Spinal Cord Anatomy

18

Spinal Reflex or Reflex Arc

Reflexes are automatic response initiated by some external

stimulus Also known as a _______ ____—a nerve pathway that carries out

a reflex Receptor activated→ sensory neuron→ dorsal root→ dorsal

cord→ interneuron→ ventral cord→ motor neuron→ _________ (muscle or gland)

19

Autonomic Nervous System (ANS)

Autonomic NS under involuntary and unconscious control Controls smooth muscle, internal organs and glands of body

Have motor components only Sensory neurons in somatic nerves carry information about state of

organs to CNS ANS divided into two parts – ____________ and Parasympathetic

component Innervate all internal organs of body

20

Diagram of Sympathetic and Parasympathetic Divisions of the Autonomic Nervous System

Both parts of ANS made of 2 motor neurons—______________ and _______________ neurons

Note: Autonomic nervous system only has one pathway—i.e. from CNS to some organ or tissue

___________ neurons in the sympathetic division are myelinated when exit from CNS→ synapses with _____________ fibers

21

which are made of un-myelinated neurons innervating target organ (has cell body in sympathetic ganglion outside of CNS)

_____________________ has long and myelinated pre-ganglionic fibers and short and un-myelinated post-ganglionic fibers.

Sympathetic System

Associated with “fight or flight” response Activates during emergency situations—_____________________ E.x. dilates bronchi and increases heartbeat, slows down digestion

Axons exit cord and run to ganglia near the cord where synapse with post synaptic or second motor neurons whose cell bodies lies within the ________________________ found in the sympathetic trunk

Neurotransmitter released by postganglionic neuron is usually

____

Parasympathetic System

Promotes internal body responses associated with relaxation Neurotransmitter on postganglionic neuron is usually ______ Cell bodies of pre-synaptic neurons of parasympathetic system exit

from medulla and from sacral regions of spinal cord

22

synapse with post-synaptic neurons occur near or inside target organs

Note: most but not all organs innervated by both systems—e.g. adrenal medulla and sweat glands for example are only innervated by the sympathetic division of the ANS.

Central Nervous System

spinal cord allows communication between brain and spinal nerves

as well as being centre for reflex actions both are also protected by 3 coverings called the ____________ different layers of meninges sandwiched together and contain

cerebrospinal fluid between them—functions as a cushion against trauma

csf also found in _____________ of spinal cord and __________ of brain (brain has four ventricles—2 lateral, a 3d and a 4th) as well as the sub-arachnoid space.

____ functions in variety of ways such as: protection of CNS from injury when jarred by acting as shock absorber and cleansing the CNS of metabolic wastes and then reabsorbed back in bloodstream

23

_______________ = infection of meninges→ can be serious

Meninges

Parts of Brain24

brain made of many different structures: ___________ (medulla, pons and midbrain), __________, _________, _____________, __________ cortex (also called ____________)

1. Brain Stem Made of medulla, pons and midbrain Primitive brain

Diagram of Brain

Medulla

25

regulates heartbeat (through A.N.S.), breathing (through chemoreceptors as discussed in respiratory system) and vasoconstriction (through pressure receptors)

contains connections to spinal cord and higher brain centres

Pons important connection between cerebellum and spinal cord as

well as higher brain centres such as cerebral cortex

helps regulate breathing rate along with medulla

Midbrain

also a reflex centre for visual, auditory and tactile responses

2. Diencephalon

Regulates body functions and emotions

26

a) Hypothalamus Regulates hunger, sex drive, sleep, thirst, body

temperature, water balance, and blood pressure Controls pituitary gland (part of endocrine system)—thus

it is a link between nervous and endocrine system Makes ____ (vasopressin) and _________ by

______________________ which are passed onto and stored in posterior pituitary gland

Connection between hypothalamus and posterior pituitary

27

Notice how neurosecretory cells in hypothalamus terminate in posterior part of pituitary gland and secrete hormones into blood stream

b) Thalamus

Regulates states of sleep and arousal or wakefulness (damage to it causes coma)

3. Pituitary gland

Referred to as the “master gland” because it controls many of the functions of other glands of body

Made of ________ and _________ pituitary

28

Axon endings of hypothalamus in posterior pituitary store ____ (antidiuretic hormone) or ___________ (ADH) made by hypothalamus

Also stores _________ (also made in hypothalamus)—causes contraction of uterus and release of milk from mammary glands

Diagram of Pituitary Gland

4. Cerebellum

processes info from inner ear and send impulses to muscles to maintain balance

has outer layer of gray matter and inner layer of white matter

29

Diagram of Cerebellum

5. Cerebrum Higher brain centre Responsible for consciousness Outer layer called _________ _____ and contains grey

matter (cell bodies and short unmyelinated fibres) Made of 2 halves—_____ and ____ cerebral hemispheres Joined together by densely packed nerve bundle called

_____________ _____________ Cerebrum divided into frontal, temporal, parietal and

occipital lobes

Parts of Cerebrum

30

folded cortex has increased surface area has ______ areas that initiate and control voluntary movement ______ areas are areas that receive and process sensory

information _____________ areas are places in cerebrum where integration of

information occurs. They deal with higher consciousness, learning, memory, intellect and artistic ability; they relay information on actions for your body to take

Diagram of Association Areas of Cortex

Basal nuclei _________________________________________

31

Adrenal Glands & Fight or Flight Response

Made of inner ________ and outer ________ Stimulated directly by ANS and indirectly by hypothalamus Hormones produced by adrenal cortex are released during times of

stress-- _____________ , ___________ and some sex hormones– regulate amount of minerals and glucose in blood

Adrenal medulla controlled by ANS Adrenal medulla produces ____________ (adrenaline) and

_______________ (noradrenaline)

32

Effects of Epinephrine and Norepinephrine:a. ↑ metabolic rateb. ↑ blood glucose levelsc. Bronchioles dilated. Rate of breathing ↑e. Blood vessels of skin and digestive tract constrict while

those in skeletal muscles dilatef. Heart rate ↑ and cardiac muscle contracts with more force

Above help get one ready for emergency

33