Subdivisions of Nervous System

Subdivisions of Nervous System

Gray and White Matter

• Gray matter = neuron cell bodies, dendrites, and synapses

– forms cortex over cerebrum and cerebellum and central portion of spinal cord.

– forms nuclei deep within brain

• White matter = bundles of axons

– forms tracts that connect parts of brain.

– Ascending and descending tracts in the spinal cord.

Fiber Tracts in White Matter• White Matter: Fibers and

tracts that allow for communication to/from and between the various cortical areas– Commissures – connect

corresponding gray areas of the two hemispheres

• (Corpus Collusum)– Projection fibers – enter the

hemispheres from lower brain or cord centers

• Sensory neurons project up to the cortex.

• Motor descend away from the cortex.

Fiber Tracts in White Matter

– Association fibers – connect different parts of the same hemisphere.

– I.e. You see a tiger on the loose. You get and get scared because visual association fibers project to many areas of the brain including the limbic system and motor system.

Meninges

• Dura mater: outermost, tough membrane– outer periosteal layer

against bone– where separated from

inner meningeal layer forms dural venous sinuses draining blood from brain

• Arachnoid layer:– subarachnoid space were

cerebral spinal fluid flows• pia mater:

– is thin layer in direct contact with brain tissue

• The three types of functional areas are:– Motor areas – control voluntary movements.

• Innervates striated muscle

– Sensory areas – conscious awareness of sensation

• Receives sensory (afferent input from the eyes, ears , skin, muscles and joints)

– Association areas – integrate various areas of the brain.

• They give context and meaning to various sensory input based on previous experience.

Functional Areas of the Cerebral Cortex

Cerebral Cortex

• The cortex – superficial gray matter; accounts for 40% of the mass of the brain

• It enables sensation, communication, memory, understanding, and voluntary movements

• Each hemisphere acts contralaterally (controls the opposite side of the body)

• No functional area acts alone; conscious behavior involves the entire cortex

• Frontal – voluntary motor functions – planning, mood, smell and social judgement

• Parietal – receives and integrates sensory information

• Occipital – visual center of brain

• Temporal – areas for hearing, smell, learning, memory,

emotional behavior

Functions of Cerebrum - Lobes

Functional Regions of Cerebral Cortex

Primary Motor Cortex

Located on precentral gyrus. Initiates motor responses that control voluntary muscles of speech and movement. The entire body is mapped here. Considered the pyramidal motor system.

Motor Control

• Precentral gyrus (primary motor area) relays signals to spinal cord to supply muscles of opposite side

• Motor homunculus - proportional to number of muscle motor units in a region– Greater # of motor units

allows for fine movement patterns.

• Face, mouth, hands, feet

Supplemental Motor/Pre Motor Cortex

Located just anterior to precentral gyrus. Involved with controlling and planning learned movement responses. SMC controls sequence of movements from memory .Supplemental motor cortex driven by intention while pre motor cortex appears to be driven to movements guided by a visual cues. May effect the primary motor cortex directly or directly contribute to the cortical spinal tract.(15%)

Prefrontal Cortex

• The highest developed part of the brain. Involved in higher thought processes such as judgment, working memory, personality, abstract thinking.

• Closely linked to the limbic system (emotions)

• Movement requires the input from many cortical areas.

Sensory Perception• Specific receptors for touch, pressure, stretch,

temperature, and pain transmit afferent impulses from the external environment to the cortex

• Somatosensory area in postcentral gyrus

Sensory Homunculus

• Area of cortex dedicated to sensations of body parts is proportional to the sensitivity of that body part (# of receptors)– The face mouth ,hands and feet have the greatest amount of receptors

which allows the greatest discrimination of touch.

Speech Areas

• Wernicke’s Area: Sensory in nature

• involved in speech comprehension – Damage results in receptive

aphasia

• Broca’s Area: involved in speech production.

• Coordinates respiratory and oral movements – Damage results in expressive

aphasia

Functions of the limbic system: learning emotion appetite (visceral function),sex and endocrine integration.Key structures include: 1. Hippocampus: learning and memory2. Amygdala: processing emotions such as fear. (emotional memory)3. Hypothalmus: regulate autonomic endocrine and visceral functions. 4. Ventral Tegmental Area: (VTA) Area in midbrain containing nuclei that have dopamine containing neurons involved endogenous reward center.

Reticular Formation of Midbrain

• Midbrain – Reticular Formation

regulates sleep, wakefulness and arousal

• Reflex Orientation to sensory stimulus – Visual

• Superior colliculi

– Auditory• inferior colliculi

Cerebellum

• Cerebellum– Compares descending

cortical input to ascending proprioceptive (sensory) input and figure out the most efficient way to move.

– Critical for the timing of learned skilled motor programs

– It can make online changes to motor programs on the

– Helps us maintain muscle tone, posture, and smooth muscle contractions

• Distinguish pitch and similar sounding words

Anatomy of the Spinal Cord

• Cylinder of nerve tissue within the vertebral canal (thick as a finger)– vertebral column grows faster so in an adult the

spinal cord only extends to L1-2

• 31 pairs of spinal nerves – 8 cervical (C1-C8)– 12 thoracic (T1-T12)– 5 Lumbar (L1-L5)– 5 Sacral (S1-S5)– 1 Coccygeal (C0)

Functions of the Spinal Cord• Conduction

– bundles of fibers passing information up and down spinal cord

• Locomotion– repetitive, coordinated actions of several muscle groups– central pattern generators are pools of neurons providing

control of flexors and extensors (walking)

• Reflexes– involuntary, stereotyped responses to stimuli (remove

hand from hot stove)– involves brain, spinal cord and peripheral nerves

Meninges of Vertebra and Spinal Cord

Cross-Sectional Anatomy of the Spinal Cord

• Central area of gray matter shaped like a butterfly and surrounded by white matter in 3 columns

• Gray matter = neuron cell bodies with little myelin• White matter = myelinated axons

Gross Anatomy of Lower Spinal Cord

• The amount of white matter relative to grey matter decreases as you move down the cord.– Cervical :lots of white

matter, ventral horn enlargements.

– Thoracic: small dorsal and ventral horns. Intermediate horn for the sympathetics in the body,

– Lumbar: Round cord, ventral horn enlargements

– Sacral: Small round cord, almost no white matter.

Peripheral Nerves• Consist of 31 pairs of

spinal nerves and 12 cranial nerves.

• They extend from both the brain and spinal cord to their effecter organ.

• ganglion = groups of cell bodies in a nerve that are located outside the (CNS)

Anatomy of a Nerve

• A nerve is a bundle of nerve fibers (axons)• Epineurium covers nerves, perineurium surrounds a

fascicle and endoneurium separates individual nerve fibers

Anatomy of Ganglia in the PNS

• Cluster of neuron cell bodies in nerve in PNS is the dorsal root ganglion

• Sensory (afferent) divisions (receptors to CNS)– visceral sensory( messages from organs) allow our CNS

to interpret internal environments. – somatic sensory division ( messages from skin, joints,

muscles) allow our CNS to interpret both our external environments.

• Motor (efferent) division (CNS to effectors) response to the environment through excitation of: – visceral motor division (ANS) Involuntary

effectors: cardiac, smooth muscle, glands• sympathetic division (fight or flight)• parasympathetic division (rest and digestion)

– somatic motor division (voluntary) effectors: skeletal muscle

Functional Divisions of PNS

Cranial Nerves

• 12 pairs of cranial nerves originate from the base of the brain • They control a variety of functions relating to the head, neck, and

internal organs• Why do we care about their functions and what does it mean if there are

deficits in one or more cranial nerves?

Autonomic Nervous System• Motor nervous system controls glands, cardiac

and smooth muscle – also called visceral motor system

• Regulates unconscious processes that maintain homeostasis– BP, body temperature, respiratory airflow

• ANS actions are automatic– biofeedback techniques

• train people to control hypertension, stress and migraine headaches

Divisions of ANS• Two divisions innervate same target organs

– may have cooperative or contrasting effects

1. Sympathetic division ( Fight and Flight)– prepares body for physical activity or any kind of stress!

• increases heart rate, BP, airflow to organs vital for dealing with the stress( skeletal muscles, heart brain), blood glucose levels to ensure you have enough fuel to get out of trouble, etc– If you are chased by a tiger he won’t be very sympathetic

2. Parasympathetic division (Rest and Digest)– calms many body functions and assists in rest and

restoration functions such as digestion and waste elimination.

• Decreased heart rate, BP and blood will be shunted away from skeletal muscles and towards vital organs i.e. intestinal tract.

Somatic Nervous vs. Autonomic Nervous Division

• Motor pathways of the somatic division consist of a single motor neuron that extends from the spinal cord to skeletal muscle.

• Motor pathways of the ANS consist of a two neurons between the brain or spinal cord and the effector – the preganglionic begins in the brain or spinal cord

and extends to a ganglion (soma of postganglionic neuron)

– the postganglionic neuron which extends from the ganglion to an effector organ

Motor Pathways of the Somatic Nervous Division vs. Autonomic Nervous Division

Efferent Sympathetic vs. Parasympathetic

Ganglia and Abdominal Aortic Plexus

Adrenal Glands• Paired glands sit on superior pole of each kidney• Cortex (outer layer)

– secretes Aldosterone, Cortisol, gonadocorticoids • Medulla (inner core)

– a modified sympathetic ganglion • stimulated by preganglionic sympathetic neurons

– secretes neurotransmitters (hormones) into blood• catecholamines (85% epinephrine and 15%

norepinephrine)• The result is:

– an increase in blood glucose levels via glycogenolysis and gluconeogenesis in the liver

– the vasoconstriction of blood vessels and redirecting blood flow toward the brain, heart and skeletal muscles.

– Increase in heart rate and stroke volume

Sympathetic and Vasomotor ToneFight and Flight: Sympathetic division prioritizes blood vessels to skeletal muscles and heart in times of emergency. Blood will be shunted away from digestive tract.

During times of resting or digesting vasoconstriction of vessels to the skeletal muscles and dilatation of the vessels of the digestive tract.

Dual Innervations of the Iris

• ANS has membrane receptors to both ACh and NE

• Depending on which neurotransmitter is released– PNS releases of ACH from its

postganglionic neuron which will cause the pupils to constrict.

– The SNS causes the release of NE from the postganglionic neuron. That will bind to its receptor causing the opposite ( pupils dilate)

• The heart :– NE increases both force and

rate of heart contraction– ACh decreases both force and

rate heart contraction.