1. Chapter 9: Nervous System

2. Functions Sensors Processing Effectors
Monitor external and internal environment
Processing
Receives information, integrates it, and decided what to do
Effectors
Carries messages to effectors and tells them what to do

3. Types of Nervous Cells Neurons Neuroglial Main cell of nervous tissue
Relay and process messages
Neuroglial
Provide support to the neurons
Several types known
Ex: Schwann, microglial

4. Neuroglial Cells Microglial cells Oligodendrocytes Schwann cells
Scattered throughout CNS
Phagocytize bacteria or cellular debris
Oligodendrocytes
Along nerve fibers
Provide myelin sheath (made of a fatty substance called myelin) around axon in CNS
Schwann cells
Same as oligodendrocytes but in PNS

5. Neuroglial Cells (cont)
Astrocytes
Provide connection between a neuron and a blood vessel
Provide support, help regulate ion concentrations in tissue, make-up scar tissue after injury
Ependymal cells
Forms epithelial-like linings on the outsides of specialized parts or lining cavities within the CNS

7. Neurons Remember: It’s a cell! Body of neuron Cell Structures
Cell Body – contains cell organelles
Dendrites- carry messages to cell body
Axons – carry messages away from cell body
Cell Structures
Large nucleus with easily seen nucleolus
Chromatophilic substance – similar to rough ER
Scattered throughout cytoplasm, membranous
Neurofibrils- help support cell shape

10. Axons Can be myelinated or unmyelinated PNS CNS
Schwann cells form myelin sheath
Nodes of Ranvier- small breaks in myelin sheath
CNS
Oligodendrocytes form myelin
Myelinated neurons form white matter
Unmyelinated neurons form gray matter

12. Structural Classification of Neurons
Multipolar
Many small branched dendrites
One axon
Found in CNS
Bipolar
Two processes off of cell membrane (one axon and one dendrite)
Neurons in special sense organs
Unipolar
One process off of cell body (one axon)
Found throughout PNS

14. Functional Classification of Neurons
Sensory (afferent) neurons
Have sensitive dendrites that are stimulated by changes in environment
Message is taken into CNS
Usually unipolar or sometimes bipolar
Interneurons
Transfer, direct, and process messages within CNS
Usually multipolar
Motor (efferent) neurons
Carries message out of CNS to effectors

16. A Neuron at Rest Inside the neuron Outside the neuron Result
High in K+
High in negative ions
Outside the neuron
High in Na+
High in positive ions
Result
K+ tends to diffuse out
Na+ tends to diffuse in
Negative ions cannot cross

18. A Neuron at Rest (cont)
Na/K pump - helps to restore concentration gradient across the cell membrane
Resting potential - difference is electrical charge across the membrane
Established by concentration gradients of various ions
Inside of the membrane has a negative charge of 70 mv
Membrane is said to be polarized

19. Potential Changes
Stimuli cause changes to the resting potential by making the inside of the membrane less negative
Once a stimulus happens:
If stimulus is not strong enough to reach threshold potential = cell membrane will return to resting potential
If stimulus is strong enough to reach threshold potential = start an action potential
Summation - when additive effect of stimuli causes action potential

21. Action Potential Starts at trigger zone of axon
Threshold stimulus open sodium channels
Sodium moves into axon
Because of the concentration gradient
Because of the negative charge that attracts the positive ions
Depolarizes the membrane as negative charge diminishes
Potassium channels open and potassium moves out of the axon, repolarizing the membrane
Animation #1 Animation #2

22. Action Potential Animation

23. Nerve Impulse
Action potential at the trigger zone stimulates the next part of the axon to do a action potential
Potentials spread along the axon like a wave
Unmyelinated axons
Wave continues uninterrupted; relatively slow
Myelinated axons
Wave goes through saltatory conduction (jump from one node to the next); very fast
Animation

24. Neuron Responses All-or-nothing effect
Neuron does not react until a threshold stimulus is applied, but once it is applied it reacts fully
Stimuli greater than threshold levels don’t change the size of the response but changes its frequency
Refractory period:
After a action potential
Brief period of time
The nerve cannot be stimulated again.

25. The Synapse The connection between two neurons
Don’t touch, separated by synaptic cleft
One-way communication between axon of presynaptic neuron and dendrite of postsynaptic neuron
Neurotransmitters are made in the synaptic knob of the axon, stored in synaptic vesicles, and cross the cleft when needed

27. Neurotransmitter Actions
Excitatory Action:
A neurotransmitter that puts a neuron closer to an action potential (facilitation) or causes an action potential
Inhibitory Action:
A neurotransmitter that moves a neuron further away from an action potential
Response of neuron:
Responds according to the sum of all the neurotransmitters received at one time

28. Neurotransmitters Acetylcholine Monoamines – modified amino acids
Neuropeptides- short chains of amino acids
Depression:
Caused by the imbalances of neurotransmitters
Many drugs imitate neurotransmitters
Ex: Prozac, zoloft, alcohol, drugs, tobacco

29. Release of Neurotransmitters
When an action potential reaches the end of an axon, Ca+ channels in the neuron open
Causes Ca+ to rush in
Cause the synaptic vesicles to fuse with the cell membrane
Release the neurotransmitters into the synaptic cleft
After binding, neurotransmitters will either:
Be destroyed in the synaptic cleft OR
Taken back in to surrounding neurons (reuptake)
Animation

30. Neuronal Pools
Groups of highly interconnected neurons that work together in the CNS
Convergence
Axons from different parts of the nervous system connect to the same neuron combining their affects
Divergence
A message from one neuron is sent to many neurons at once; amplifies message

31. Divergence
Convergence

32. Nerves Nerves are made of bundled axons, called nerve fibers
Sensory (afferent)- carry messages to CNS
Motor (efferent)- carry messages from CNS to effectors
Nerves
Same definitions hold true
Most nerves contain both types of fibers and are called mixed nerves

33. Structure of a nerve
A nerve fiber (axon) is surrounded with endoneurium
Nerve fibers are bundled together and surrounded with perineurium to form a fascicle
Fascicles are bundled together and surrounded with epineurium to form a nerve

34. Nerve Pathways Path that the message takes through the body Includes:
Sensor
Sensory neuron
Interneuron
Motor neuron
Effector

35. Reflex Arc Simplest nerve pathway is a reflex Reflexes without pain
Involve only sensory and motor neurons
Ex: knee-jerk reflex
Reflexes with pain
Involve interneurons in CNS
Ex: withdrawal reflex

37. The CNS Central nervous system Consists of brain and spinal cord
Made of both gray and white matter
Covered in meningies

38. The Meninges (Brain) Cranial Bone Dura mater Arachnoid mater
First layer; tough, fibrous connective tissue
Forms inner periosteum of cranial bone
Folds into the cranium in some places to form division walls in the brain
Arachnoid mater
Web-like membrane over CNS
Does not dip into crevices

40. The Meninges (Brain) Subarachnoid space Pia mater
Below arachnoid layer
Contains cerebrospinal fluid
Pia mater
Lower layer of meninges
Forms a tight covering over brain
Does dip into crevaces

42. Meningies (Spinal Cord)
Same except:
Vertebrae bones - protection
Epidural space- filled with loose connective and adipose tissue
All other are the same

43. Cerebrospinal fluid
Flows through ventricles (spaces in brain) in the subarachnoid space, and through the central canal of the spinal cord
Fluid is made by the choroid plexus

44. Spinal Cord
Stretches from brain to intervertebral disk between first and second lumbar vertebrae
31 pairs of spinal nerves come of the cord
Gray matter core surrounded by white matter

45. Spinal Cord (cont)
Responsible for communication between brain and body and spinal reflexes
Ascending tracts
Nerves that send info to brain
Descending tracts
Nerves that send into to effectors

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48. The Brain Made up off about 100 billion neurons Four main sections:
1) Cerebrum
Nerves for processing sensory and motor function
Higher functions (like reasoning)
2) Diencephalon
Processes sensory information
3) Brainstem
Regulates certain body functions like breathing
4) Cerebellum
Coordinates skeletal muscle movements

51. Cerebrum Divided into two hemispheres: right and left Corpus callosum
Connects the two sides
Other structures
Convolutions - ridges
Sulcus - shallow groove
Fissure - deep groove

52. Areas of the Cerebrum Frontal lobe Parietal lobe Temporal lobe
Occipital lobe
Insula
Each lobe has unique functions

53. Areas of the Cerebrum (cont)
Cerebral cortex
Thin layer of gray matter surrounding cerebral hemisphere; contain most of the cell bodies in the cerebrum
Inner part of the cerebrum is mainly made of white matter

54. Functions of the Cerebrum
Motor areas
Primarily in frontal lobe
Send information out to effectors
Sensory areas
Interpret information from sensors
Area in parietal, temporal, and occipital lobes
Association areas
Analyze information from sensors
Located in areas in all lobes mentioned above

56. Diencephalon
Located between the cerebral hemispheres above the brainstem
Contains:
Thalamus
Hypothalamus
Pituitary gland
Pineal gland

57. Functions of the Diencephalon
Thalamus
Routes sensory impulses to the correct region of the cerebrum
Hypothalamus
Monitors many internal conditions, link between nervous and endocrine system
Limbic system
Thalamus, hypothalamus, and basal nuclei
Controls experience and expression (feelings)

58. Brainstem Connection between spinal cord and the rest of the brain
Contains:
Midbrain
Pons
Medulla oblongata

59. Midbrain Located between diencephalon and pons
Contains some visual and auditory reflexs
Serves as the main connection for motor neurons between spinal cord and upper part of brain

60. Pons Rounded bulge between midbrain and medulla oblongata
Relays impulses between medulla and cerebrum or between cerebrum and cerebellum

61. Medulla oblongata Lowest part of brain, connect to spinal cord
All ascending and descending tracts run through the oblongata
Serves as a control center for many vital function like heart rate, blood pressure, and respiratory center

63. Cerebellum Located in the lower back part of the brain
Structured liked cerebrum with inner white matter core and gray matter covering
Controls posture and complex skeletal movements

64. The PNS Peripheral Nervous system Includes: Divided into:
12 pairs of cranial nerves
31 pairs of spinal nerves
Divided into:
1) Somatic nervous system
Controls conscious activities; connects to skin and skeletal muscles
2) Autonomic nervous system
Controls unconscious activities; connects to internal organs or structures

66. Autonomic Nervous System
Two branches:
1) Parasympathetic
Control under more normal conditions
2) Sympathetic
Control under stress or emergency conditions (fight or flight)
Usually these have antagonistic effects
Work to counteract each other (one increases, while other decreases)
Either might be utilized to maintain homeostasis

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