The Nervous System Part 2

By the end of this class you should understand:

• The functions of the autonomic nervous system

• The three major regions of the brain and their general functions

• The layers of protection around the central nervous system

• The functions of sleep, memory and the limbic system

Brief Disclaimer:

• I am massively oversimplifying everything there is to say about the brain

• There are entire upper-division courses dedicated solely to the study of the brain– Feel free to take some! They’re awesome!

• I will now cover in 1 hour what could reasonably take 40…

Peripheral Nervous System

• The peripheral nervous system is highly organized by function– Sensory neurons bring

information to the CNS– Motor neurons bring information

from the CNS to the organs of the body

• The CNS is composed of interneurons that connect to each other and process information

Somatic vs. Autonomic

• Somatic motor neurons are voluntary– They innervate (attach to)

skeletal muscles• Autonomic motor

neurons are involuntary– They innervate the heart,

liver, digestive organs– They also innervate glands

that release hormones

Autonomic Nervous System

• The autonomic nervous system is further subdivided into two branches:– Sympathetic nervous system– Parasympathetic nervous system

• These two branches work against each other– Sympathetic: “fight or flight”– Parasympathetic: “rest and digest”

Autonomic Nervous System

Sympathetic vs. Parasympathetic

• Sympathetic nervous system increases blood flow to muscles, heart and lungs– Response to fear and to exercise

• Parasympathetic nervous system increases blood flow to liver, kidneys and digestive organs– Dominates before/during/after eating food unless

blocked by sympathetic

Autonomic Neurotransmitters• Sympathetic nerve fibers

release neurotransmitters called norepinephrine– One of its major functions is to

stimulate the adrenal glands to release a hormone called epinephrine

– The resulting hormone rush is more commonly known as adrenaline

• Parasympathetic nerve fibers release acetylcholine, the same as somatic motor nerves

Brain vs. Body

• People often believe that the brain and the body are separate– The “car” model of brain activity

• The reality is that the brain’s state, including emotions, is affected by the body and in turn affects the body– The sympathetic nervous system

activates even when you are looking at someone attractive or get excited about something

Central Nervous System

• The central nervous system processes incoming information from all sensory neurons– Most of this processing

is done in the brain– The spinal cord does

some processing, as in reflexes

Brain Regions

• Forebrain– Site of conscious and

emotional processing of information

• Midbrain– Reflexive processing and

control of senses• Hindbrain– Controls basic motor and

homeostatic functions– Common to all vertebrates

Brain Regions

Parts of the Forebrain

• The cerebral cortex– AKA the cerebral hemispheres– Made of five lobes (only three covered here)– Dedicated to processing sensory information,

making decisions, and creating emotions

• The diencephalon– Responsible for regulating the brain’s and the

body’s activity• Thalamus and hypothalamus

Cerebral Cortex• Frontal lobes– Site of active decisions and

short-term memory– Hyperdevelops during puberty,

responds to social input, is not fully mature until the mid-20s• C.f. Teenager behavior and

Phineas Gage• Occipital lobes– Dedicated entirely to processing

visual information• Parietal lobes– Initiates voluntary movement

and sensation of touch

Diencephalon• The thalamus is a major

component of the brain situated directly below the cerebral cortex– All sensory information comes

through the thalamus before reaching the cerebral cortex• Exception: sense of smell has direct

line to limbic system!• The hypothalamus is the body’s

thermostat for hunger, thirst, and temperature– Also controls activity of the

autonomic nervous system

Midbrain• The midbrain has many functions we take for granted– Regulates wakefulness– Creates visual reflexes– Coordinates senses with movement of head– Processes unconscious reflexes related to standing and

moving

Hindbrain• The hindbrain has two regions

– Cerebellum: coordinates timing on firing of motor neurons and helps store muscle memory

– Brain stem: attaches to spinal cord and sends and receives information, also manages breathing and heart rate

• The hindbrain is often called the “reptilian brain” since even the simplest vertebrates have a similar brain

CNS Protection• The entire central

nervous system has four layers of protection:– Bone (skull and

vertebral column)– Cerebrospinal fluid

(helps protect and support weight)

– Meninges (connective tissue layers)

– Blood-brain barrier

Blood-Brain Barrier

• The most common type of neuroglial cell in the CNS is called the astrocyte

• Astrocytes tightly seal the blood vessels entering the CNS and only permit vital nutrients to pass through– Restrict access of bacteria and toxins

• Anything that affects the brain must be able to diffuse through astrocyte cell membranes– What chemicals can diffuse through a

cell membrane?

Selected Functions of the Brain• Sleep– A period of unconsciousness during which brain

activity changes and regenerates the brain– Without sleep, death will occur within two weeks

• Emotion– Activity in the limbic system in response to stimuli– In constant back-and-forth communication with the

frontal lobe (consciousness)• Memory– Created and processed in the frontal lobe, there are

many types of memory

Sleep• There are two types of sleep:– Rapid-Eye Movement sleep

(REM sleep)– Non-Rapid-Eye Movement sleep

(Non-REM or NREM sleep)• REM sleep is most vital to brain

function– Most dreams occur during REM

sleep– During REM sleep, body is

paralyzed• Sleepwalking occurs during NREM

dreams

Limbic System• Limbic system produces

emotions in response to stimuli such as sex hormones, stress hormones, hunger hormones, body senses, and information from the frontal lobe– Essentially a parallel

consciousness– Animals with no frontal lobe

activity (including infants) behave solely on limbic information

Types of Memory

• Short-term memory can only retain a few pieces of information at a time

• If the information is repeated, emphasized or attached to other information it may be stored in long-term memory– One aspect of sleep is the process of reorganizing memory

• The frontal lobe also stores motor memory in collaboration with the cerebellum

• The limbic system also has its own limbic memory for retaining emotional information (for example, trauma)

See you next week!

• Also next week’s lab will be the nerve lab!• Come prepared to cut up some sheep brains!– Morning lab will start approx. an hour late, sorry!