Human SystemsNervous, Endocrine, Reproductive

The Nervous SystemOH MY!!!

Receive sensory information from various receptors & then interpret & process the information.

If a response is needed some portion of the brain or spinal cord initiates a response = motor response.

The cells that carry this information are neurons

THE CENTRAL NERVOUS SYSTEM- CNSCONSISTS OF THE BRAIN AND SPINAL CORD

Spinal Nerves:•There are 31 pairs•Emerge from the spinal cord•Some are motor nerves & some are sensory nerves

Cranial Nerves:• There are 12 pairs• Emerge from the brain stem of the brain•EX: optic nerve pair (carry visual information from retina to the brain)

COMPARE THE ORGANIZATION OF NERVOUS SYSTEMS

What the heck do they do differently?

• Sensory neurons: transmit information from external stimuli and internal conditions.– Send the info to the CNS.

• Interneurons: analyze & interpret sensory input

• Motor neurons: motor output leaves through these & communicate with effector cells.

• Effector cells: muscle cells or endocrine cells.

Typical Pathway of Nervous System

Explain in as much detail as possible the pathway if you should touch something hot.

As soon as you touched the pot of boiling water a sensory receptor began an action potential or “nerve impulse”.

Each receptor in your body is designed to transform a particular kind of stimulus into an action potential

There are a chain of neurons which take the impulse towards the CNS. In this case the spinal cord.

Once at the spinal cord the action potential is routed to the appropriate area of the CNS for interpretation.

During its stay in the CNS the action potential is carried by interneurons.

Your brain has now made the decision to remove your hand.

Relay neurons send the action potential to the spinal cord & out one of the spinal nerve pairs (motor neuron).

The motor neuron is taking the impulse/action potential to the muscle and a chemical signal is sent to the muscle (effector cells) which results in a contraction, moving your hand.

Junction where a neuron sends a chemical to muscle tissue is called: motor end plateThe name for the muscle (in

this case) is the effector.

The Mad Mad Neuron Competition!!!

Nervous system pathway is a one way road from dendrite to synaptic terminals.

Functions• Dendrites: receive signals• Axon: transmits signals• Synapse terminals: location where

neurotransmitters are released• Neurotransmitters: chemical messengers that

travel out of the presynaptic neuron and into the postsynaptic neuron.– Ex: acetylcholine, epinephrine, norepinephrine,

dopamine, serotonin, and GABA

Neurons of Vertebrates & Most Invertebrates

• Have cells that are helper cells to the neurons called: Glial or glia cells– Nourish neurons, insulate the axons, & regulate

the extracellular fluid around the neurons.– Outnumber the neurons in the mammalian brain

10-50 fold.– During a synapse some neurotransmitters are sent

to the glial cells to be metabolized for fuel

Types of Glia Cells

Astrocytes: facilitate info. Transfer at synapses & sometimes release neurotransmitters. cause nearby blood vessels to dilate enabling neurons to receive oxygen &

glucose faster. They also regulate extracellular concentrations of ions & neurotransmitters.

Schwann cells & oligodendrocytes: cover axons with a myelin sheath which provide electrical insulation.Microglia: protect against pathogens.

What is a nerve impulse?• Nerve impulse is misleading. We will call it an action

potential instead• Can be measured in the same way as electricity is

measured– Voltage

• Millivolts

• The conductor of a neuron is the axon– Is covered by a myelin sheath

• Increases the rate at which an action potential passes down an axon.

• Membrane potential: the electrical potential difference across the plasma membrane.

Resting potential

• Area of a neuron that is ready to send an action potential but is not currently sending one.

• This area is considered polarized– Characterized by the active transport of sodium ions (Na+

) out of the axon cell & potassium ions (K+) into the cytoplasm.

– There are negatively charged ions permanently located in the cytoplasm

– This collection of charged ions leads to a net positive charge outside the axon membrane & negative charge inside.

Neuron at Resting Potential

Resting potential results from the diffusion of K+ and Na+ through channels that are always open (ungated)

There are also gated ion channels• Stretch-gated ion

channels: in cells that sense stretch

• Ligand-gated ion channels: located at synapses & open/close for a specific chemical.

• Voltage-gated ion channels: located in axons & open/close when membrane potential changes.

Action Potential

• Described as a self-propagating wave of ion movements in and out of the neuron membrane

• This is the diffusion of the Na+ & the K+ .– Sodium channels open & then potassium ones do to.

• This is the “impulse” or action potential• It is a nearly instantaneous event occurring in one area of the

axon = depolarization– This area initiates the next area on the axon to open up the channels.

• This action continues down the axon.

• Once an impulse is started at the dendrite end that action potential will self-propagate itself to the far axon end of the cell.

Depolarization opens the activation gates on most Na+ channels, while the K+ channels activation gates remain closed. Na+ influx makes the inside of the membrane positive with respect to the outside.

The activation gates on the Na+ and K+ channels are closed, & the membrane’s resting potential is maintained.

A stimulus opens the activation gates on some Na+ channels. Na+ influx through those channels depolarizes the membrane. If the depolarization reaches the threshold, it triggers an action potential.

The inactivation gates on most Na+ channels close, blocking Na+ influx. The activation gates on most K+ channels open, permitting K+ efflux which again makes the inside of the cell negative.

Both gates of the Na+ channels are closed, but the activation gates on some K+ channels are still open. As these gates close on most K+ channels, & the inactivation gates open on Na+ channels, the membrane returns to its resting state.

Return to Resting Potential

• Remember that one neuron may send dozens of action potentials in a very short period of time.

• Once an area of the axon sends an action potential it cannot send another until the Na+ & K+ have been restored to their positions at the resting potential.

• Active transport is required to move the ions = repolarization– The time it takes for a neuron to send an action

potential & then repolarize is called: the refractory period of that neuron.

Inside of membrane becomes more -

Inside of membrane becomes less -

What makes it go faster:

• Different sized axons– Bigger = faster

Saltatory conduction: By jumping from one node to the next, this increases the conduction velocity, allowing the signal to travel faster

FUNCTIONS OF THE BRAIN

How do neurons communicate with each other?This occurs through a chemical communication called a synapse.

-examples of chemicals: acetylcholine, epinephrine, dopamine, norepinephrine, serotonin, and GABA

Different communication synapse pattern may occur…

7.5 The neurotransmitters binding to the receptor protein initiates to ion channel opening and Na+ diffusing in which starts the action potential down the postsynaptic neuron

9.5 The neurotransmitter is broken down by enzymes & is released from the receptor protein. They will diffuse back across the synaptic gap.

9.75Sodium channel closes

Usually a ligand-gated channel

Generations of Postsynaptic Potentials• Neurotransmitters which generate action potentials are

known as Excitatory Neurotransmitters.– Cause Na+ to diffuse into the postsynaptic neuron– EX: acetocholine

• Neurotransmitters which prohibit action potentials are known as Inhibitory Neurotransmitters.– Causes hyperpolarization of a neuron by allowing Cl- move

across postsynaptic cell into the membrane or cause K+ to move out of the postsynaptic cell

– EX: GABA

Acetylcholine• Common neurotransmitter to vertebrates &

invertebrates.• Helps with muscle stimulation, memory formation,

learning, heart rate, energy level.• Released by motor neurons• If it remained in the synapse, the postsynaptic

neuron would keep “firing” indefinitely.– Acetylcholinesterase breaks down the acetylcholine in

the synapse.• Read article about acetylcholine and nicotine

Decision making

• A neuron is on the receiving end of many excitatory and inhibitory stimuli.

• The neuron sums up the signals– If the sum is excitatory the axons will “fire”– If the sum is inhibitory the axons will not

• The summation of the messages is the way decisions are made by the central nervous system.

Controlling the Signaling System

• Some synapses have neurotransmitters bind to metabotrophic receptors instead of ion channels

• Activates a signal transduction pathway in the postsynaptic neuron involving a 2nd messenger.– Have a slower onset but last longer– Modulate the responsiveness of postsynaptic neurons

in diverse ways.• EX: altering the number of open channels

In animals, internal & external signals regulate a variety of physiological responses that

synchronize with environmental cycles and cues.

Circadian rhythms

THE MOUSE PARTY

The Nervous System & The Endocrine System

Work cooperatively in order to ensure homeostasis.

The Endocrine System

Glands that secrete hormones as a chemical signal which is sent to different parts of your

body.Helps maintain homeostasis

What are hormones?

• Chemical messengers that have a physiological effect far from where they originated.

• They travel through the bloodstream• Most are under the control of a negative

feedback mechanism.– Exceptions: oxytocin (positive feedback mechanism)

Homeostatic control of body temperature

Negative feedback: physiological changes that bring a value back closer to a set point.

Message is sent by thermoreceptors

Difference between neurotransmitters & endocrine signals

• Neurotransmitters: usually small, nitrogen-containing compounds that are conveyed from one specialized nerve cell to another along specific nerve highways throughout the body & are designed to elicit immediate responses.

• Endocrine signals: usually hormone secreted from glands that use blood vessels to disperse their signal molecules, to elicit a slower response.

Just to mess with you a little…

• Neurosecretory cells (aka neurohormones)-– Nerve cells that release hormones

• A few chemicals serve as both hormones and chemical signals.– EX: epinephrine/adrenaline & norepinephrine• “fight or flight” hormone produced in adrenal gland• Serves as a neurotransmitter

Maintaining Blood Glucose Levels• Our cells rely on glucose for cellular respiration• Therefore our cells are acting to lower the glucose in our

blood• The increase and decrease of our glucose levels never

stops• From the villi in the intestines glucose is passed the

capillary beds into the hepatic portal vein which takes the blood directly to the liver where the glucose is converted to glycogen.

Maintaining Blood Glucose Levels

• The hepatic portal vein is the only major blood vessel where the blood glucose concentration changes in large degrees.– Other blood vessels receive the blood after it has been

acted upon by the hepatocytes (liver cells )

• Hepatocytes take direction by two hormones:– Insulin– glucagon

Both produced in the pancreas & have opposite effects on blood glucose concentrations

INSULIN• Produced by β(beta) cells in the pancreas when

blood glucose levels are high.

• It “hooks up” with body cells & causes them to open protein channels which allow the glucose to diffuse (facilitated) into the cells

– In the liver & muscles, insulin stimulates the hepatocytes to take in glucose and convert it to glycogen.

GLUCAGON

• Produced by α(alpha) cells in the pancreas when blood glucose levels are low.

• When released into the bloodstream this molecule stimulates the hydrolysis the granules of glycogen in the liver cells and muscles cells.

Maintaining Blood Glucose Levels

Diabetes• A disease characterized by hyperglycemia– High blood glucose

TYPES OF DIABETES

Type I Type II

β cells do not produce enough insulin Body cell receptors do not respond properly to insulin= insulin resistance

Can be controlled by the injection of insulin Can be controlled by diet

Autoimmune disease- immune system attacks β cells & destroys them

Less than 10% of diabetics have this type. Most common form of diabetes - 90%

Most often occurs in children & young adults Associated with genetic history, obesity, lack of exercise, advanced age, & certain ethnic groups

• Steroid hormones:– Example is estrogen– Function: increases thickness of uterine lining

• Peptide hormones:– Example is insulin– Function: stimulates glucose uptake by body cells

• Tyrosine Derivative hormone:– Example is thyroxin– Function: increases metabolic rate

Types of Hormones & Their Function

Steroid Hormones• Synthesized from cholesterol & classified as lipids• Easily passes through cell membrane• Once in cytoplasm binds with receptor protein– Forms hormone receptor complex

• Then passes through nuclear membrane & binds to certain genes– It will then either inhibit or induce transcription

• They control the production of proteins in a target cell

• Are protein molecules• When it reaches its target cell it binds with a

receptor protein on the outer surface of the cell– No receptor protein on surface of cell it isn’t a

target cell• A secondary messenger molecule is triggered

into action in the cytoplasm• Never enter the cell

Peptide Hormones

Sometimes the glands come in

pairs…

Sometimes they are alone…

Major Endocrine Glands

Hypothalamus & The Pituitary Gland

• Hypothalamus largely controls the pituitary gland

The pituitary gland is actually a pair Anterior & posterior lobes

The anterior & posterior lobes of the pituitary gland communicate differently with the hypothalamus

Posterior lobe of the pituitary gland

Contain axons of cells called neurosecretory cells that extend

from the hypthalamus to the posterior lobe of the pituitary

These hormones are produced within the hypothalamus but secreted from the posterior pituitary.

Anterior Lobe of The Pituitary Gland

Hormones (called releasing hormones) produced in the hypothalamus are transported through capillary beds to the portal vein which goes to the anterior pituitary.

These hormones target cells are the anterior pituitary cells

They cause the anterior pituitary to secrete specific hormones

Antidiuretic Hormone (ADH) Secretion

• Controls how much water is reabsorbed from the collecting duct back into the bloodstream.– If ADH is secreted, the collecting duct

becomes permeable to water & water leaves by way of osmosis into the highly hypertonic medulla of the kidney.

– Water is then reabsorbed back into the bloodstream

- If ADH is not secreted, the collecting duct remains impermeable to water

- Urine will then contain a high amount of water.

REPRODUCTION

HUMAN REPRODUCTION (sexual reproduction): sperm, egg, & fertilization ensures genetic

variation in our species.

Male Reproductive System

Testosterone: Male Hormone

• Determines the development of male genitalia during embryonic development

• Ensures development of secondary sex characteristics during puberty.

• Maintains the sex drive of males throughout their lifetime.

Bladder

Urethra

Vagina

Clitoris

Uterus

Ovary

Oviduct (Fallopian Tube)

Cervix

Rectum

The menstrual cycle

• Starts at puberty• It’s a hormonal cycle lasting for ~28 days– Times the release of the ovum (egg) • For fertilization & implantation

• The inner lining of the uterus (endometrium) grows thick (becomes highly vascular)

• If no implantation then blood vessels breakdown (menstruation)

FSH- follicle stimulating hormone

LH- luteinizing hormone

Graafian follicle

Oocyte + zona pellucida (glycoprotein coat)

For 10-12 days

What are the hormone levels at ovulation?

FSH, LH & estrogen= highProgesterone = low

Gonadotrophin releasing hormone

Hormone Origin Target Causation

GnRH Hypothalamus Anterior pituitary gland

Production of FSH & LH

FSH Anterior pituitary gland

Ovaries Stimulate follicle growth & production of oestrogen

LH Anterior pituitary gland

Ovaries Stimulate follicle growth & production of oestrogen

Oestrogen Ovaries Endometrium Make endometrium highly vascular

Progesterone Corpus luteum Endometrium Maintains endometriums highly vascular state

Complete this chart

Hormones involved in the female menstrual cycle.

During ovulation what is happening with the 4 hormones?

LH: is highFSH: is highEstrogen: is highProgesterone: low

What is happening with the hormones during menstruation?

All are low except FSH

As long a progesterone is being produced the endometrium will not break down.

The hypothalamus will not produce GnRH as long as progesterone levels & estrogen levels are high.

Therefore FSH and LH will remain at non conducive levels to produce any other Graafian follicle.

Once the corpus luteum begins to break down this lowers the levels of progesterone and estrogen which signals the hypothalamus to secrete GnRH

Natural Fertilization

• Occurs in the fallopian tubes 24-48 hours after ovulation

• Zygote begins dividing and has divided many times by the time it reaches the uterus for implantation.

• As long as the endometrium is in a highly vascular state, implantation will occur.

Problems couples may face with having a baby

• Low sperm count (in males)• Failure to achieve or maintain an erection• Do not ovulate regularly• Blocked fallopian tubes

One way to solve the problem…• In-vitro fertilization:– Female is injected with FSH for 10 days• Ensures development of several Graafian follicles

– Several eggs are harvested surgically– Male ejaculates into a container– Harvested eggs are mixed with the sperm– Observed under a microscope to determine which

eggs have been fertilized and are mitotically dividing normally.

– 2 to 3 embryos are placed in the female uterus– Leftovers are frozen & used later, if needed.

Ethical issues concerning IVFFOR

• Allows couples who normally would not be able to have children to have them.

• Unhealthy embryos are eliminated for consideration

• Genetic screening can be done prior to implantation

AGAINST• Embryos not used are either frozen

or destroyed• Legal issues with regards to unused

embryos if there is a divorce.• Genetic screening at embryo state

could lead to choosing desirable characteristics

• IVF bypasses natures way of decreasing the genetic frequency of that reproductive problem

• IVF increases the chances of multiple births & with it the problems associated with multiple births.

Reproduction & rearing of offspring require free energy beyond that used for maintenance & growth.

Reproductive strategies in response to energy availability

• Food availability and ambient temperature determine energy balance, and variation in energy balance is the ultimate cause of seasonal breeding in all mammals and the proximate cause in many. Photoperiodic cueing is common among long-lived mammals from the highest latitudes down to the mid-tropics.