ANATOMY OF NECK AND BACK

Dr.Hardik Rathod

The fact that humans can walk upright on two legs is because they have what other animals don’t, the spine. Human spine is made up of vertebral column which contains various vertebral bodies. Inside the vertebral column is a spinal canal which contains a spinal cord, which basically connects human brain with the rest of the body.

WHAT IS ITS ROLE IN OUR BODY?

• It forms the central AXIS of the body

• It SUPPORTS and carries the weight of body above pelvis

• It PROTECTS the spinal cord within spinal canal

• It maintains the POSTURE and MOVEMENT of your  body

ANATOMY

In a human’s vertebral column, there are normally thirty-three vertebrae the upper twenty-four are articulating and separated from each other by intervertebral discs, and the lower nine are fused in adults, five in the sacrum and four in the coccyx, or tailbone

The human spine is divided in five regions 1) Cervical spine 2) Thoracic spine 3) Lumbar spine 4) Sacrum 5) Coccyx

There are seven cervical vertebrae, twelve thoracic vertebrae, and five lumbar vertebrae , 5 fused sacral and 4 fused coccygeal vertebras.

1) Cervical Spine or the Neck

• Neck part of spine is made up of 7 cervical vertebras and it supports the head and also brings about the movement.

• The movement of nodding the head takes place predominantly through flexion and extension at the atlanto-occipital joint between the atlas and the occipital bone.. This movement between the atlas and occipital bone is often referred to as the “yes joint”, owing to its nature of being able to move the head in an up-and-down fashion.

• The movement of shaking or rotating the head left and right happens almost entirely at the joint between the atlas and the axis, the atlanto-axial joint. A small amount of rotation of the vertebral column itself contributes to the movement. This movement between the atlas and axis is often referred to as the “no joint”, owing to its nature of being able to rotate the head in a side-to-side fashion.

2) Thoracic vertebra column

• Made up of 12 vertebras

• They give attachment to thoracic cage which protects and covers heart and other internal organs

• Brings about the movement of chest when you are breathing

• Not much movement occurs here

3) LUMBAR VERTEBRA

• 5 Lumbar vertebras

• Largest and thickest of all vertebras

• Carry the weight of whole body above legs

• Helps in bending  forwards and laterally

4) SACRUM AND COCCYX

• Rudimentary fused vertebras

• Connect the spine to pelvis via sacroiliac joints

Spinal curves

When viewed from the side, an adult spine has a natural S-shaped curve. The neck (cervical) and low back (lumbar) regions have a slight concave curve, and the thoracic and sacral regions have a gentle convex curve.

The curves work like a coiled spring to absorb shock, maintain balance, and allow range of motion throughout the spinal column

• An abnormal curve of the lumbar spine is lordosis, also called sway back.

• An abnormal curve of the thoracic spine is kyphosis, also called hunchback.

• An abnormal curve from side-to-side is called scoliosis.

Vertebrae

• Vertebrae are the 33 individual bones that interlock with each other to form the spinal column. The vertebrae are numbered and divided into regions: cervical, thoracic, lumbar, sacrum, and coccyx .

• Only the top 24 bones are moveable; the vertebrae of the sacrum and coccyx are fused. The vertebrae in each region have unique features that help them perform their main functions.

•Cervical (neck) - The main function of the cervical spine is to support the weight of the head. The seven cervical vertebrae are numbered C1 to C7. The neck has the greatest range of motion because of two specialized vertebrae that connect to the skull. The first vertebra (C1) is the ring-shaped atlas that connects directly to the skull. This joint allows for the nodding or “yes” motion of the head. The second vertebra (C2) is the peg-shaped axis, which has a projection called the odontoid, that the atlas pivots around. This joint allows for the side-to-side or “no” motion of the head.

• Thoracic (mid back) - the main function of the thoracic spine is to hold the rib cage and protect the heart and lungs. The twelve thoracic vertebrae are numbered T1 to T12. The range of motion in the thoracic spine is limited.

• Lumbar (low back) - the main function of the lumbar spine is to bear the weight of the body. The five lumbar vertebrae are numbered L1 to L5. These vertebrae are much larger in size to absorb the stress of lifting and carrying heavy objects.

• Sacrum - the main function of the sacrum is to connect the spine to the hip bones (iliac). There are five sacral vertebrae, which are fused together. Together with the iliac bones, they form a ring called the pelvic girdle.

• Coccyx region - the four fused bones of the coccyx or tailbone provide attachment for ligaments and muscles of the pelvic floor.

Intervertebral discs

• Each vertebra in your spine is separated and cushioned by an intervertebral disc, which keeps the bones from rubbing together.

• Discs are designed like a radial car tire. The outer ring, called the annulus, has crisscrossing fibrous bands, much like a tire tread.

• These bands attach between the bodies of each vertebra. Inside the disc is a gel-filled centre called the nucleus, much like a tire tube

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• Discs are designed like a radial car tire. The outer ring, called the annulus, has crisscrossing fibrous bands, much like a tire tread.

• These bands attach between the bodies of each vertebra. Inside the disc is a gel-filled centre called the nucleus, much like a tire tube

• Discs function like coiled springs. The crisscrossing fibers of the annulus pull the vertebral bones together against the elastic resistance of the gel-filled nucleus.

• The nucleus acts like a ball bearing when you move, allowing the vertebral bodies to roll over the incompressible gel. The gel-filled nucleus contains mostly fluid.

• This fluid is absorbed during the night as you lie down and is pushed out during the day as you move upright.

• With age, our discs increasingly lose the ability to reabsorb fluid and become brittle and flatter; this is why we get shorter as we grow older.

• Also diseases, such as osteoarthritis and osteoporosis, cause bone spurs (osteophytes) to grow.

• Injury and strain can cause discs to bulge or herniate, a condition in which the nucleus is pushed out through the annulus to compress the nerve roots causing back pain.

Muscles

• The two main muscle groups that affect the spine are extensors and flexors.

• The extensor muscles enable us to stand up and lift objects. The extensors are attached to the back of the spine.

• The flexor muscles are in the front and include the abdominal muscles.

• These muscles enable us to flex, or bend forward, and are important in lifting and controlling the arch in the lower back.

• The back muscles stabilize your spine. Something as common as poor muscle tone or a large belly can pull your entire body out of alignment. Misalignment puts incredible strain on the spine.

Facet joints

The facet joints of the spine allow back motion. Each vertebra has four facet joints, one pair that connects to the vertebra above (superior facets) and one pair that connects to the vertebra below (inferior facets).

Spinal cord

• The spinal cord is about 18 inches long and is the thickness of your thumb.

• It runs from the brainstem to the 1st lumbar vertebra protected within the spinal canal.

• At the end of the spinal cord, the cord fibers separate into the cauda equina and continue down through the spinal canal to your tailbone before branching off to your legs and feet.

• The spinal cord serves as an information super-highway, relaying messages between the brain and the body.

• The brain sends motor messages to the limbs and body through the spinal cord allowing for movement. The limbs and body send sensory messages to the brain through the spinal cord about what we feel and touch. Sometimes the spinal cord can react without sending information to the brain.

• These special pathways, called spinal reflexes, are designed to immediately protect our body from harm.

• Any damage to the spinal cord can result in a loss of sensory and motor function below the level of injury.

• For example, an injury to the thoracic or lumbar area may cause motor and sensory loss of the legs and trunk (called paraplegia). An injury to the cervical (neck) area may cause sensory and motor loss of the arms and legs (called tetraplegia, formerly known as quadriplegia).

Spinal nerves

• Thirty-one pairs of spinal nerves branch off the spinal cord. The spinal nerves act as “telephone lines,” carrying messages back and forth between your body and spinal cord to control sensation and movement.

• Each spinal nerve has two roots. The ventral (front) root carries motor impulses from the brain and the dorsal (back) root carries sensory impulses to the brain.

• The ventral and dorsal roots fuse together to form a spinal nerve, which travels down the spinal canal, alongside the cord, until it reaches its exit hole - the intervertebral foramen.

• Once the nerve passes through the intervertebral foramen, it branches; each branch has both motor and sensory fibers.

• The smaller branch (called the posterior primary ramus) turns posteriorly to supply the skin and muscles of the back of the body. The larger branch (called the anterior primary ramus) turns anteriorly to supply the skin and muscles of the front of the body and forms most of the major nerves.