here's the bottom line...
​   receptor > integrator > effector
   (afferent)                         (efferent)
   (sensory)                           (motor)

           the limbic system

it shares extensive neural pathways with other brain regions so it is often considered a "connecting hub of emotions, sensation, and action" along with regulating executive functions, motor control, memory, and learning. 

bipolar disorder

  amygdala

Parkinson's disease is a neurodegenerative disorder that affects dopaminergic (dopamine producing) neurons.  the cause is unknown. Alpha-synuclein is a protein found in these neurons. In PD,  the protein folds incorrectly and results in clumps called Lewy Bodies. The current hypothesis is that Lewy bodies are toxic to these neurons and may even get passed along from one neuron to the next which causes the spread of the disease. 

cingulate gyrus helps to regulate our response to fearful or unpleasant experiences and the prediction and avoidance of negative consequences associated with these stimuli.  it serves to help us avoid  negative stimuli via the recall of associated memories. 

    central nervous system (CNS):
​                           the brain

Alzheimer's disease

   thalamus

The hippocampus is a  embedded deep into temporal lobe and plays a central role in learning and memory.

 hypothalamus and stress...

 the cingulate gyrus covers the
corpus callosum.
it processes emotions,
regulates behavior regulation and various autonomic motor functions.

Alzheimer's disease is caused by
​the build-up of proteins called 
 amyloid plaques in the brain.
Another protein called tau forms tangles within brain cells.

Research suggests that the
 brains of people with bipolar disorder may differ from the brains of people who do not have this condition. Medical providers
diagnose and treat based on symptoms and history and not
 brain imaging. Research also suggests that bipolar disorder is linked to the presence of specific genes. Individuals who have a parent or sibling with bipolar disorder have an increased chance of having the disorder themselves. 

 the amygdala is a mass of gray matter inside each cerebral hemisphere. it is associated with
the experiencing of emotions and is responsible for processing scary and threatening stimuli.
it's only 0.3% of the volume of the human brain yet is controls many of our emotional responses. 

The Nervous System

The mammillary bodies are associated with recall/memory. Recall begins in with the activation of neurons in the hippocampus. memories
are relayed through the fornix to the mammillary bodies 

hypothalamus

reflexes

The thalamus relays >95% of  sensory info to the cortex!
That's all of the vision, taste, touch and balance info but not sensory info from the nose. The olfactory bulb sends that info directly to the cerebrum by the olfactory peduncle.

             cool brain info...

  the limbic system dictates the emotional and behavioral responses centered around survival such as reproduction, caring for offspring, feeding and the fight or flight response by regulating the endocrine and autonomic responses to emotional stimuli. it is also involved with establishing and accessing memories and reinforcing learned behavior. the structures of the limbic system serve to link the cerebral cortex's consciousness with the autonomic, unconscious brain stem...

A stroke occurs when the brain's blood supply is reduced or stopped. this prevents the brain from receiving necessary nutrients/O2 and the brain cells post blockage die. 

types are: hemorrhagic
           ischemic

Depression can manifest as temporary episodes of sadness all the way up to persistent depression. major depression or major depressive disorder is also called clinical depression. it's different from being depressed due to an episodic event such as a death in the family. This severe form of depression is diagnosed using the APA's Diagnostic and Statistical Manual of Mental Disorders (DSM-5)

0.1% of the population in the US has MS. that number increases to 2.5 to 5%  if you have a sibling or parent with MS. there is a genetic link but factors other than genetics are at play. An identical twin has a 25% chance of developing MS if their twin is affected. 

Clinical depression

Parkinson's disease

    Peripheral Nervous System/ PNS

The thalamus is located just above the brain stem between the cerebral cortex and the midbrain. It serves to relay motor and sensory info to the cerebral cortex as well as regulating alertness/wakefulness and sleep. 
​The spinothalamic tract is a sensory pathway that originates in the spinal cord, relaying info to the thalamus about discomfort ie...itch, temperature...pain. 

 first-order neurons:
 carry signals from the   periphery to the spinal cord. 
 
  second-order neurons:
 carry signals from the spinal   cord to the thalamus.

 third-order neurons:
 carry signals from the   thalamus to the primary
 sensory cortex.

neurological disorders include:
multiple sclerosis, Alzheimer's disease, Parkinson's disease, epilepsy, stroke, clinical depression, bipolar disorder

pathologies

multiple sclerosis/MS

  cingulate gyrus

The fornix is a bundle of nerve fibers that serve as an efferent relay from the hippocampus. The fornix also relays some afferent fibers to the hippocampus from the diencephalon. 

The hypothalamus serves as a link between the nervous and the endocrine system via the the pituitary gland. Specialized neuron clusters called neurosecretory cells release hormones that direct the pituitary gland to in turn release hormones.
Example:
the hypothalamus secretes thyrotrophin releasing hormone (TRH). This triggers the pituitary gland to secret thyroid stimulating hormones (TSH) which is released into the blood. The thyroid gland has receptors for this hormone which informs the thyroid gland to release thyroid hormone. Thyroid hormones are essential for metabolic homeostasis. See the negative feedback loop to the right. Other hormones released by the hypothalamus include corticotrophin-releasing hormone, dopamine, growth hormone-releasing hormone, somatostatin and gonadotrophin-releasing hormone. 

when a threat  is perceived, either real or aroused  by memories or fear, 
 the amygdala automatically activates the fight-or-flight response. it's activation, triggered by emotions like fear, anxiety or aggression, causes the release of stress hormones that serve to prep yourself to fight or run away. 

There's a third system not mentioned in this diagram. We discuss it when we explore digestion. The enteric nervous system (ENS) is a network of nervous tissue located in the walls of the digestive tract. It coordinates many visceral activities without the direction of the CNS although the ANS does exert some influence over this system. There are as many neurons in the ENS (1 x 10*8) as the spinal cord and this system uses familiar neurotransmitters, such as serotonin which plays a vital role in the gut and brain connection. 

central nervous system: ​the spinal cord

The mammillary bodies are part of the diencephalon. paired mammillary bodies are found on the inferior surface of the hypothalamus.  Serving as relay nuclei, they forward information from the hippocampus to the thalamus to aid in memory consolidation. 

Stroke

    peripheral nerve structure

  the structures of the limbic system include the:
1. amygdala
2. cingulate gyrus
3. thalamus
4. mammillary bodies/fornix
5. hypothalamus
6. hippocampus

reflex arc:
a reflex arc consists of a receptor, an integrator and an effector.
sensory cells carry (afferent impulses) to an interneuron in the
spinal cord which sends a response to the motor neuron. 

MS = multiple sclerosis
is an autoimmune disease whereby the immune system degrades myelin. this causes nerve relay problems between the CNS and PNS and a deterioration of nerves.
symptoms of MS vary, depending  on the level of damage and the # of nerves affected. although there isn't a cure for MS, there are therapeutics which can manage symptoms. 

bipolar disorder (called also
manic depression) is a condition that exhibits severe high and low mood swings and changes in behavior. it is common f or people with this disorder to feel elated
and energized and then have  periods of feeling hopeless.

As the primary efferent tract of the hippocampus, the fornix relays information from the hippocampus to the mammillary bodies and on to the to the thalamus.

Although MS is an autoimmune disease, the cause of multiple sclerosis is unknown. Both genetics and environmental factors are thought to be responsible. there are associated risk factors including:
sex: twice as may women as men are affected
family history of the disease
infections: several viruses including Epstein-Barr, have been related to onset
race: those of Northern European descent are at highest risk 
climate. MS is more common in  areas with temperate climates
vitamin D: low levels of vitamin D/
low exposure to UV
other autoimmune diseases

mammillary bodies/fornix/hippocampus

There is an inherited predisposition to developing depression. depression can also be caused by physical illness, aging and  gender.

    autonomic nerve relay